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WORKS  TRANSLATED  BY 
DR.    GEORGE    K.    BURGESS 

PUBLISHED    BY 

JOHN  WILEY  &  SONS. 

Thermodynamics  and  Chemistry. 

A  Non-Mathematical  Treatise  for  Chemists  and 
Students  of  Chemistry.  By  P.  DUHEM,  Corre- 
spondant  de  1'Institut  de  France,  Professor  of 
Theoretical  Physics  at  the  -  University  of  Bor- 
deaux. Authorized  Translation  by  GEORGE  K. 
BURGESS,  Docteur  de  1'Universiu*  de  Paris,  As- 
sistant Physicist,  Bureau  of  Standards.  8vo, 
xxi  +  445  pages,  139  figures.  Cloth,  $4.00. 

High-Temperature  Measurements. 

By  H.  LE  CHATELIER,  Ingenieur  en  chef  du  Corps 
des  Mines,  Professor  de  chimie  mine'rale  au  >  ol- 
lege  de  France,  and  O.  BOUDOUARD,  Assistant, 
College  de  France.  Translated  by  GEORGE  K. 
BURGESS,  D.Sc.  (Paris),  Assistant  Physicist,  Bu- 
reau of  Standards.  Second  Edition,  Revised  and 
Enlarged.  12010,  xv  +  34i  pages,  79  figures. 
Cloth,  $3.00. 


Frontispiece. 


HIGH-TEMPERATURE 
MEASUREMENTS. 


BY 

H.  LE  CHATELIEK, 

Ingenieur  en  chef  du  Corps  des  Mines, 

Professeur  de  chimie  minerale  au  College  de  France, 

Editor  of  the  Revue  de  Metallurgie, 


AND 


O.  BOUDOUARD, 

Docteur  es  Sciences. 


AUTHORIZED    TRANSLATION   AND    ADDITIONS 

BY 

G.  K.  BURGESS,  D.Sc.  (PARIS), 

Assistant  Physicist,  Bureau  of  Standards. 


Of   THE 

UNIVERSITY 

Of 


SECOND  EDITI&Q£(38£B!&&AND  ENLARGED. 
FIRST   THOUSAND. 


NEW  YORK : 

JOHN  WILEY   &   SONS. 
LONDON  :  CHAPMAN  &  HALL,  LIMITED. 

1907 


Copyright,  1901,  1904, 

BT 

GEORGE  K.  BURGESS. 


ROBERT  DRT7MMOND,   PRINTER,  NEW  YORK. 


AUTHOR'S  PREFACE  TO  FIRST  AMERICAN  EDITION. 


THE  measurement  of  high  temperatures  was  considered 
for  a  long  time  to  be  a  very  difficult  operation  and  of  a 
very  uncertain  precision.  There  were  cited  with  admira- 
tion a  half-dozen  determinations  seeming  to  merit  some 
confidence.  During  the  last  few  years  the  question  has 
made  considerable  progress,  and  we  possess  to-day  several 
sufficiently  precise  pyrometers  whose  usage  is  rapidly 
spreading  among  scientific  and  industrial  laboratories. 
Before  describing  them,  perhaps  it  will  not  be  useless  to 
indicate  the  services  that  they  may  render  to  science  and 
to  industry,  by  giving  a  brief  summary  of  similar  services 
that  they  have  already  rendered. 

Among  the  researches  in  pure  science  which  result  from 
the  new  methods  of  the  measurement  of  high  tempera- 
tures, of  primary  importance  are  the  masterly  investiga- 
tions of  Osmond  on  the  allotropic  transformations  of  iron. 
After  having  precisely  determined  the  nature  of  the 
phenomenon  of  recalescence,  noted  for  the  first  time  by 
Gore  and  Bartlett,  Osmond  discovered  in  iron  two  similar 
transformations :  one,  taking  place  in  the  neighborhood  of 
750°,  corresponds  to  the  loss  of  magnetic  properties,  and 
the  other,  at  about  900°,  is  accompanied  by  a  considerable 
evolution  of  heat.  A  third  transformation  of  iron  near 

ill 


iv     AUTHOR'S  PREFACE   TO  AMERICAN  EDITION. 

1300°  has  been  discovered  since  by  Ball.  Soon  after, 
Curie  studied  by  the  same  methods  the  variation  with  the 
temperature  of  the  magnetic  properties  of  a  great  number 
of  substances,  iron  among  them,  which  possess  very 
definite  perturbations  corresponding  to  the  different  trans- 
formation-points. 

Later,  Le  Chatelier  studied  the  influence  of  temperature 
on  the  dilatation  and  electrical  resistance  of  metals.  The 
allotropic  transformations  are  recognized  by  sharp  points 
in  the  curves  of  electrical  resistance  and  by  sudden  depres- 
sions in  the  dilatation  curves. 

But  these  researches  have  not  been  limited  to  the  metals 
and  their  alloys.  Investigating  the  dilatation  of  the  differ- 
ent varieties  of  silica,  Le  Chatelier  was  led  to  the  discovery 
of  a  transformation  of  quartz  at  580°,  above  which  the 
dilatation  of  this  substance  becomes  negative,  and  to  the 
discovery,  still  more  important,  of  a  new  variety  of  silica 
distinct  from  tridymite,  but  possessing  the  same  density 
and  into  which  silex  and  even  quartz  are  transformed  by 
sufficient  heating. 

In  the  same  manner  have  been  studied  the  dissociation 
of  the  carbonate  of  lime,  the  bromide  of  barium,  of 
minium,  etc.  Similarly  the  curves  of  fusibility  of  salt 
mixtures  have  been  determined,  their  forms  indicating  the 
existence  of  definite  compounds  or  of  solid  solutions. 
Also  it  has  been  possible  to  distinguish,  among  the  natural 
products  classed  under  the  general  Jiead  clay,  a  series  of 
distinct  chemical  substances. 

Finally,  it  has  been  possible  to  pursue  the  study  of  the 
laws  of  radiation  at  high  temperatures  with  a  greater 
precision,  and  to  establish  the  theory  of  incandescent 
enclosures. 

If  we  take  up  next  the  researches  in  industrial  science, 
we  find  the  number  to  be  so  considerable  that  it  is  out  of 


AUTHOR'S  PREFACE   TO  AMERICAN  EDITION.      V 

the  question  to  attempt  to  give  in  this  short  preface  the 
complete  list.  It  will  suffice  to  mention  the  most  impor- 
tant among  them,  such  as  the  following  investigations: 

The  fusibility  of  metallic  alloys  has  been  the  object  of  a 
very  complete  memoir  by  H.  Gautier,  and  of  important 
researches  by  the  late  Sir  Roberts  Austen  and  by  Heycock 
and  Neville,  Boudouard  and  others. 

The  tempering  of  steel  has  been  examined  in  all  its 
details  by  Osmond,  Charpy,  H.  Howe,  Sauveur,  Brinnel. 

Cementation  by  Arnold. 

Crystallization  in  the  annealing  of  metals,  in  particular 
of  iron  and  brass,  observed  by  Sauveur,  Stead,  Charpy. 

And  lastly  the  considerable  number  of  researches  made 
at  the  laboratory  of  the  Ecole  des  Mines  on  the  dilatation 
of  ceramic  pastes  and  of  glass,  by  Damour,  Chatenet, 
Grenet,  Coupeau,  Chautepie. 

Precise  methods  for  the  measurement  of  high  tempera- 
tures are  not  limited  to  laboratory  researches,  however, 
but  have  rapidly  penetrated  into  industrial  practice.  A 
series  of  investigations  by  Le  Chatelier  first  made  known  the 
exact  temperatures  entering  into  the  various  metallurgical 
operations;  and  to-day,  in  the  greater  number  of  steel- 
works, the  tempering  and  the  annealing  of  the  great 
forged  pieces,  cannons,  plates,  are  no  longer  made  without 
the  aid  of  pyrometers,  doing  away  with  the  workman's 
judgment,  formerly  alone  consulted. 

In  glass  manufacture  Damour  has  introduced  the  em- 
ployment of  pyrometers  for  controlling  the  large  furnaces 
and  recipients,  and  for  the  regulating  of  the  temperature 
of  the  annealing-chambers. 

Parville  has  done  the  same  for  the  porcelain  industry, 
where  the  use  of  fusible  cones  allowed  the  determination 
of  the  stopping-point  of  the  heating  but  gave  no  contin- 
uous indications  necessary  to  regulate  the  time  of  heating, 


VI     AUTHOR'S  PREFACE  TO  AMERICAN  EDITION. 

and  on  this  last  depends  in  a  large  measure  the  quality  of 
the  products  obtained,  and  above  all  the  cost  of  fuel. 

In  the  manufacture  of  chemical  products  the  precise 
measurements  of  temperature  render  to-day  very  great 
services;  for  instance,  in  the  Deacon  process  for  the 
making  of  chlorine,  whose  yield  varies  very  greatly  for 
slight  changes  of  temperature.  Ludwig  Mond  in  England 
and  the  St.  Gobian  Company  in  France  have  the  merit  .of 
having  first  utilized  these  new  scientific  methods. 

Euchene  of  the  Paris  Gas  Company  controlled  all  the 
details  of  the  manufacture  of  gas  by  numerous  measure- 
ments of  temperature. 

But  the  most  remarkable  of  these  industrial  applications 
have  been  made  in  England  under  the  lead  of  Sir  Roberts 
Austen  by  applying  photographic  recording  to  the  indica- 
tions of  the  thermoelectric  pyrometer.  Such  installations 
at  the  Clarence  Works  of  Sir  Lothian  Bell  and  at  the  blast- 
furnaces of  Dowlais  give  a  continuous  record  of  the  tem- 
perature of  the  draft  and  of  the  escaping  gases. 

These  very  considerable  results  have  been  obtained 
within  less  than  ten  years,  although  the  new  methods  of 
temperature  measurement  were  known  as  yet  to  only  a  few 
scientists  and  engineers.  It  is  plausible  to  suppose  that 
their  influence  on  the  progress  of  science  and  industry  will 
be  still  greater  during  the  coming  years. 

In  finishing  this  preface,  allow  me  to  thank  Dr.  G.  K. 
Burgess  for  having  taken  the  trouble  to  translate  into 
English  our  little  volume.  His  science  and  his  competence 
are  for  us  a  certain  guarantee  of  cordial  reception  by 
American  and  English  readers. 

H.  LE  CHATELIER. 

PARIS,  January  10,  1901. 


PREFACE  TO  SECOND  EDITION. 


THE  subject  of  pyrometry  has  advanced  very  rapidly 
in  recent  years,  and  in  preparing  a  new  edition  of  the 
HIGH  TEMPERATURE  MEASUREMENTS,  it  has  been  necessary 
to  completely  revise  the  work.  This  revision  has  been 
made  by  the  translator  at  the  request  of  Prof.  Le  Chatelier, 
and  the  plan  followed  has  been  to  leave  the  original  text 
intact  as  far  as  possible  and  to  insert  the  results  of  recent 
work  hi  the  appropriate  chapters,  all  of  which  have  been 
so  modified. 

The  greatest  advances  have  been  made  in  optical  py- 
rometry, and  the  chapter  on  this  subject  has  been  greatly 
extended  and  preceded  by  one  on  the  laws  of  radiation. 
This  material  is  largely  taken  from  a  paper  *  by  Drs.  Waid- 
ner  and  Burgess,  and  the  latter  desires  to  express  his 
indebtedness  to  Dr.  Waidner  for  permission  to  use  this 
material. 

Considerable  additions  have  been  made  to  the  chapters 
on  Electrical  Resistance,  Thermoelectric  and  Gas  Pyrom- 
etry. Brief  descriptions  have  been  added  of  some  other 
pyrometers  which  have  been  considerably  used  in  the 
industries,  especially  in  the  United  States.  The  impor- 

*  C.  W.  Waidner  and  G.  K.  Burgess:  Optical  Pyrometry,  Bulletin 
of  the  Bureau  of  Standards,  1,  No.  2,  1904. 

vii 


viii  PREFACE   TO    SECOND  EDITION. 

tance  of  standardizing  pyrometers  has  been  emphasized 
by  a  special  chapter  devoted  to  that  subject. 

The  translator  wishes  to  express  his  thanks  to  those 
who  have  aided  him  by  suggestions  or  data,  and  especially 
to  Dr.  Heraeus,  Prof.  H.  M.  Howe,  Dr.  Waidner,  and  Mr. 
Whipple  of  the  Cambridge  Company. 

GEO.  K.  BURGESS. 
WASHINGTON,  September  6,  1904. 


CONTENTS. 


PAGE 

PREFACE  TO  FIRST  EDITION iii 

PREFACE  TO  SECOND  EDITION.  .  vii 


INTRODUCTION. 

THERMOMETRIC  SCALES 3 

FIXED  POINTS 6 

PYROMETERS.  .  9 


CHAPTER  I. 
NORMAL  SCALE  OF  TEMPERATURES. 

LAWS  OF  MARIOTTE  AND  GAY-LUSSAC 12 

GAS-THERMOMETERS 13 

REGNAULT'S  EXPERIMENTS 16 

RESULTS  OBTAINED  BY  CHAPPUIS 20 

NORMAL  SCALE  OF  TEMPERATURES 22 

THERMODYNAMIC  SCALE 26 

CHAPTER  II. 
NORMAL  THERMOMETER. 

SEVRES  THERMOMETER 36 

CALLENDAR'S  THERMOMETER 42 

THERMOMETER  FOR  HIGH  TEMPERATURES 47 

fx 


X  CONTENTS. 

CHAPTER  III. 
GAS-THERMOMETER. 

PAGE 

SUBSTANCE  OF  THE  BULB 49 

PLATINUM 49 

IRON 51 

PORCELAIN 51 

GLASS 54 

QUARTZ 54 

CORRECTIONS  AND  CAUSES  OF  ERROR 56 

CONSTANT-VOLUME  THERMOMETER 56 

CONSTANT-PRESSURE  THERMOMETER 62 

VOLUMETRIC  THERMOMETER 64 

EXPERIMENTAL  RESULTS 66 

POUILLET'S  RESEARCHES 66 

E.  BECQUEREL'S  RESEARCHES 69 

RESEARCHES  OF  SAINTE-CLAIRE-DEVILLE  AND  TROOST.  . .  69 

VIOLLE'S  RESEARCHES 71 

RESEARCHES  OF  MALLARD  AND  LE  CHATELIER 74 

RESEARCHES  OF  BARUS 75 

RESEARCHES  OF  HOLBORN  AND  WIEN 76 

HOLBORN  AND  DAY'S  INVESTIGATIONS 77 

EXPERIMENTS  OF  JACQUEROD  AND  PERROT 79 

ARRANGEMENT  OF  EXPERIMENTS 79 

INDUSTRIAL  AIR-PYROMETERS 81 

INDIRECT  METHODS 82 

METHOD  OF  CRAFTS  AND  MEIER 82 

METHODS  OF  H.  SAINTE-CLAIRE-DEVILLE 83 

METHOD  OF  D.  BERTHELOT 86 

CHAPTER  IV. 
CALORIMETRIC  PYROMETRY. 

PRINCIPLE 91 

CHOICE  OF  METAL 92 

PLATINUM 92 

IRON 92 

NICKEL,  . ,  93 


CONTENTS.  xi 

PAGE 

CALORIMETERS 94 

WATER- JACKETED  CALORIMETERS 95 

SIEMENS  CALORIMETER 97 

PRECISION  OF  MEASUREMENTS 97 

CONDITIONS  OF  USE 99 

CHAPTER  V. 
ELECTRICAL-RESISTANCE  PYROMETER. 

PRINCIPLE 101 

INVESTIGATIONS  OF  SIEMENS 101 

RESEARCHES  OF  CALLENDAR  AND  GRIFFITHS 102 

INVESTIGATIONS  OF  HOLBORN  AND  WIEN 103 

LAW  OF  VARIATION  OF  PLATINUM  RESISTANCE 104 

NOMENCLATURE 107 

USE  AS  A  STANDARD 110 

EXPERIMENTAL,  ARRANGEMENTS 110 

SOME  RESULTS  OBTAINED 112 

SOURCES  OF  ERROR 114 

HEATING  OF  THERMOMETERS  BY  THE  MEASURING  CUR- 
RENT   114 

LAG  OF  THE  PLATINUM-THERMOMETER 114 

INSULATION ......  114 

COMPENSATION  FOR  RESISTANCE  OF  LEADS 115 

PYROMETERS  HAVING  DIFFERENT  VALUES  OF  d 116 

CHANGES  IN  THE  CONSTANTS 118 

CONDITIONS  OF  USE 119 

CHAPTER  VI. 
THERMOELECTRIC  PYROMETER. 

PRINCIPLE 120 

EXPERIMENTS  OF  BECQUEREL,  POUILLET,  AND  REGNAULT.  . .  120 

EXPERIMENTS  OF  LE  CHATELIER 122 

HETEROGENEITY  OF  WIRES 122 

CHOICE  OF  THE  COUPLE 124 

a.  ELECTROMOTIVE  FORCE 124 

6.  ABSENCE  OF  PARASITE  CURRENTS 126 

c.  CHEMICAL  CHANGES..  .  126 


xii  CONTENTS. 

PAGE 

METHODS  OF  ELECTRIC  MEASUREMENTS 128 

METHOD  OF  OPPOSITION.  . 128 

PRINCIPLE  OF  THE  METHOD 130 

USE  OF  A  POTENTIOMETER 131 

COMPENSATION  METHOD 133 

GALVANOMETRIC  METHOD 133 

RESISTANCE  OF  COUPLES 133 

GALVANOMETERS 135 

DIFFERENT  TYPES  OF  GALVANOMETER 139 

REQUIREMENTS  OF  INDUSTRIAL  PRACTICE 144 

ARRANGEMENT  OF  WIRES  OF  THE  COUPLE 146 

JUNCTION  OF  THE  WIRES 146 

INSULATION  OF  THE  COUPLE 147 

COLD  JUNCTION 151 

GRADUATION 152 

FORMULA 153 

FIXED  POINTS 156 

RECENT  RESEARCHES 162 

ELECTRIC  HEATING 163 

HOLBORN  AND  DAY'S  WORK 164 

INDUSTRIAL  APPLICATIONS 167 

CONDITIONS  OF  USE • 168 

IRIDIUM-RUTHENIUM  COUPLE  OF  HERAEUS .  168 


CHAPTER  VII. 
LAWS  OF  RADIATION. 

GENERAL  PRINCIPLES 171 

TEMPERATURE  AND  INTENSITY  OF  RADIATION 171 

EMISSIVE  POWERS 172 

THE  BLACK  BODY  OF  KIRCHOFF 173 

EXPERIMENTAL  REALIZATION 173 

REALIZATION  IN  PRACTICE 176 

BLACK-BODY  TEMPERATURE 176 

LAWS  OF  RADIATION 177 

STEFAN'S  LAW 177 

LAWS  OF  ENERGY  DISTRIBUTION 179 

WIEN'S  LAWS 181 

APPLICATIONS  TO  PYROMETRY.  .  .185 


CONTENTS.  xiii 

CHAPTER  VIII. 
HEAT-RADIATION  PYROMETER 

PAGE 

PRINCIPLE 187 

POUILLET'S  EXPERIMENTS  188 

EXPERIMENTS  OF  VIOLLE 190 

WORK  OF  ROSETTT 191 

EXPERIMENTS  OF  WILSON  AND  GRAY 194 

LANGLEY  AND  ABBOT'S  EXPERIMENTS 197 

CONDITIONS  OF  USE 193 

FERY'S  THERMOELECTRIC  TELESCOPE 198 

CHAPTER  IX. 
OPTICAL  PYROMETER. 

PRINCIPLE 204 

KIRCHOFF'S  LAW 204 

MEASUREMENT  OF  THE  TOTAL  INTENSITY  OF  RADIATION.  .  .  .  207 

MEASUREMENT  OF  THE  INTENSITY  OF  A  SIMPLE  RADIATION.  .  207 

OPTICAL  PYROMETER  OF  LE  CHATELIER 208 

PHOTOMETER 208 

ADJUSTMENT  OF  APPARATUS 212 

MEASUREMENTS 213 

DETAILS  OF  AN  OBSERVATION 214 

EMISSIVE  POWER 214 

MEASUREMENTS  OF  INTENSITY 216 

GRADUATION 216 

EVALUATION  OF  TEMPERATURES 220 

CALIBRATION  IN  TERMS  OF  WIEN'S  LAW 221 

PRECISION  AND  SOURCES  OF  ERROR 221 

MODIFICATIONS  OF  THE  LE  CHATELIER  PYROMETER 226 

FERY  ABSORPTION  PYROMETER 229 

WANNER  PYROMETER 229 

DESCRIPTION  AND  CALIBRATION 229 

SOURCES  OF  ERROR 232 

RANGE  AND  LIMITATIONS 235 

HOLBORN  AND  KURLBAUM,  AND  MORSE,  PYROMETERS 236 

HOLBORN  AND  KURLBAUM  FORM 237 

MORSE  FORM.  .  .241 


xiv  CONTENTS. 

PAGE 

CONDITIONS  OF  USE 242 

TEMPERATURE  OF  FLAMES 243 

MEASUREMENT  OF  THE  RELATIVE  INTENSITY  OF  DIFFERENT 

RADIATIONS 245 

USE  OF  THE  EYE 245 

USE  OF  COBALT  GLASS 246 

APPARATUS  OF  MESURE  AND  NOUEL 247 

CROVA'S  PYROMETER 249 

ACTION  OF  LIGHT  ON  SELENIUM 252 

CHAPTER  X. 
EXPANSION-  AND  CONTRACTION-PYROMETERS. 

WEDGWOOD'S  PYROMETER 253 

EXPANSION  OF  SOLIDS 256 

THE  JOLY  MELDOMETER 257 

HIGH-RANGE  THERMOMETERS 259 

CHAPTER   XI. 

FUSING-POINT,  DILUTION-,  AND  TRANSPIRATION- 
PYROMETERS. 

FUSING-POINT  PYROMETRY 261 

SEGER'S  FUSIBLE  CONES 262 

WIBORGH'S  THERMOPHONES 267 

DILUTION-PYROMETERS 268 

TRANSPIRATION-PYROMETERS 268 

CHAPTER  XII. 
RECORDING-PYROMETERS. 

RECORDING  GAS-PYROMETER 271 

ELECTRICAL-RESISTANCE  RECORDING-PYROMETER 274 

THERMOELECTRIC  RECORDING-PYROMETER 277 

DISCONTINUOUS  RECORDING 279 

CONTINUOUS  RECORDING 282 

LIGHTING  OF  THE  SLIT 283 

SENSITIVE  SURFACE 285 

MODIFICATIONS  OF  SIR  ROBERTS- AUSTEN'S  RECORDER...   291 


CONTENTS.  XV 

CHAPTER    XIII. 
STANDARDIZATION  OF  PYROMETERS. 

PAGE 

FIXED  POINTS 295 

SULPHUR 296 

ZINC 297 

GOLD 298 

SILVER 300 

COPPER 301 

PLATINUM 302 

IRIDIUM 302 

OTHER  METALS 302 

TABLE  OF  FIXED  POINTS 303 

WATER 307 

ANILINE 307 

NAPHTHALINE 307 

BENZOPHENONE 307 

METALLIC  SALTS 307 

STANDARDIZATION  OF  PYROMETERS » . . . .  308 

STANDARDIZING  LABORATORIES 309 

ELECTRICALLY  HEATED  FURNACES 310 

CHAPTER  XIV. 

CONCLUSION 312 

BIBLIOGRAPHY 319 

INDEX.  .  .  337 


HIGH  TEMPERATURES. 


INTRODUCTION. 

WEDGWOOD,  the  celebrated  potter  of  Staffordshire,  the 
inventor  of  fine  earthenware  and  of  fine  china,  was  the  first 
to  occupy  himself  with  the  exact  estimation  of  high  tem- 
peratures. In  an  article  published  in  1782,  hi  order  to 
emphasize  the  importance  of  this  question,  he  considered 
at  length  certain  matters  a  study  of  which  would  be  well 
worth  while  even  to-day. 

"The  greater  part  of  the  products  obtained  by  the 
action  of  fire  have  their  beauty  and  their  value  consider- 
ably depreciated  by  the  excess  or  lack  of  very  small  quan- 
tities of  heat;  often  the  artist  can  reap  no  benefit  from 
his  own  experiments  on  account  of  the  impossibility  to 
duplicate  the  degree  of  heat  which  he  has  obtained  before 
his  eyes.  Still  less  can  he  profit  from  the  experiments  of 
others,  because  it  is  even  less  easy  to  communicate  the 
imperfect  idea  which  each  person  makes  for  himself  of 
these  degrees  of  temperature." 

Joining  example  to  precept,  Wedgwood  made  for  his 
personal  use  a  pyrometer  utilizing  the  contraction  of  clay. 
This  instrument,  for  nearly  a  century,  was  the  only  guide 
in  researches  at  high  temperatures.  Replaced  to-day  by 
apparatus  of  a  more  scientific  nature,  it  has  been  perhaps 
too  readily  forgotten. 


HIGH  TEMPERATURES. 

Since  Wedgwood,  many  have  undertaken  the  measure- 
ment of  high  temperatures,  but  with  varying  success.  Too 
indifferent  to  practical  requirements,  they  have  above  all 
regarded  the  problem  as  a  pretext  for  learned  disserta- 
tions. The  novelty  and  the  originality  of  methods  at- 
tracted them  more  than  the  precision  of  the  results  or  the 
facility  of  the  measurements.  Also,  up  to  the  past  few 
years,  the  confusion  has  been  on  the  increase.  The  tem- 
perature of  a  steel  kiln  varied  according  to  the  different 
observers  from  1500°  to  2000°;  that  of  the  sun  from  1500° 
to  1,000,000°. 

First  of  all,  let  us  point  out  the  chief  difficulty  of  the 
problem.  Temperature  is  not  a  measurable  quantity  in 
the  strict  sense  of  the  term.  To  measure  a  length  or  a 
mass,  is  to  count  how  many  times  it  is  necessary  to  take  a 
given  body  chosen  as  a  unit  (meter,  gramme)  in  order  to 
obtain  a  complex  system  equivalent  either  as  to  length  or 
mass  of  the  body  in  question.  The  possibility  of  such  a 
measurement  presupposes  the  previous  existence  of  two 
physical  laws:  that  of  equivalence,  and  that  of  addition. 
Temperature  obeys  well  the  first  of  these  laws ;  two  bodies 
in  temperature  equilibrium  with  a  third,  and  thus  equiva- 
lent with  respect  to  exchanges  of  heat  in  comparison  with 
this  third  body,  will  also  be  equivalent,  that  is  to  say, 
equally  in  equilibrium  with  respect  to  every  other  body 
which  would  be  separately  in  equilibrium  with  one  of 
them.  This  law  allows  determination  of  temperature  by 
comparison  with  a  substance  arbitrarily  chosen  as  a  thermo- 
metric  body.  But  the  second  law  is  wanting ;  one  cannot, 
by  the  juxtaposition  of  several  bodies  at  the  same  tem- 
perature, realize  a  system  equivalent,  from  the  point  of 
view  of  exchanges  of  heat,  to  a  body,  of  different  tempera- 
ture; thus  temperature  is  not  measured,  at  least  insomuch 
as  one  considers  only  the  phenomena  of  convection. 


INTRODUCTION. 


In  order  to  determine  a  temperature,  one  observes  any 
phenomenon  whatever  varying  with  change  of  tempera- 
ture. Thus  for  the  mercury  centigrade  thermometer  the 
temperature  is  defined  by  the  apparent  expansion  of  mer- 
cury from  the  point  of  fusion  of  ice  measured  by  means  of 
a  unit  equal. to  T^7  of  the  dilatation  between  the  tempera- 
ture of  the  fusion  of  ice  and  that  of  the  ebullition  of  water 
under  atmospheric  pressure. 

Thermometric  Scales. — For  such  a-  determination  there 
are  four  quantities  to  be  chosen  arbitrarily:  the  phenome- 
non measured,  the  thermometric  substance,  the  origin  of 
graduation,  and  the  unit  of  measurement;  while  in  a  meas- 
urement properly  so  called  there  is  but  one  quantity  to 
be  arbitrarily  chosen,  the  magnitude  selected  as  unity. 
It  is  evident  that  the  number  of  thermometric  scales  may 
be  indefinitely  great;  too  often  experimenters  have  con- 
sidered it  a  matter  of  pride  for  each  to  have  his  own. 

Here  are  some  examples  of  thermometric  scales  chosen 
from  among  many: 


Author. 

Phenomenon. 

Substance 

Origin. 

Unit. 

Fahrenheit 

Dilatation 

Mercury 

jVery   cold 
1      winter 

|  1/180  Ice  to  B.  P. 

Reaumur 

•• 

«« 

Ice.  . 

1/80     "     "     " 

Celsius 

•< 

it 

1/100  "     "     " 

Wedgwood 

j  Permanent        ^ 
1      contraction  i 

Clay 

Dehydrated 

1/2400  init.  dimens. 

PouUlet 

Dilat.  at  const,  p. 

Air 

Ice 

} 

(Normal  ther.) 

Dilat.  at  const,  v. 

Hydrogen 

" 

1/100 

(Thermodyn. 
scale) 

j  Reversible         | 
/      heat  -scale       I 

Anything 

Heat  =  0 

Ice  to  ' 
boiling-point 

Siemens 

Electric  resistance 

Platinum 

Ice 

j 

The  enormous  differences  above  mentioned  in  the 
measurements  of  high  temperatures  are  much  more  the 
result  of  the  diversity  of  the  scales  than  due  to  the  errors 
of  the  measurements  themselves.  Thus  the  experiments 


4  HIGH   TEMPERATURES. 

on  solar  radiation  which  have  led  to  values  varying  from 
1500°  to  1,000,000°  are  based  on  measurements  which  do 
not  differ  among  themselves  by  more  than  25  per  cent. 

To  escape  from  this  confusion  it  was  first  necessary  to 
agree  upon  a  single  scale  of  temperatures ;  that  of  the  gas- 
thermometer  is  to-day  universally  adopted,  and  this  choice 
may  be  considered  as  permanent.  The  gases  possess,  more 
than  any  other  state  of  matter,  a  property  very  important 
for  a  thermo metric  -substance — the  possibility  of  being 
reproduced  at  any  time  and  in  any  place  identical  with 
themselves;  besides,  their  dilatation,  which  defines  the 
scale  of  temperatures,  is  sufficient  for  very  precise  measure- 
ments; finally,  this  scale  is  practically  identical  with  the 
thermodynamic  scale.  This  last  is  in  theory  more  impor- 
tant than  all  the  other  properties  because  it  is  independent 
of  the  nature  of  the  phenomena  and  of  the  substances 
employed.  It  gives,  too,  a  veritable  measure  and  not  a 
simple  comparison;  its  only  inconvenience  is  for  the 
moment  not  to  be  experimentally  'realizable,  at  least  rigor- 
ously, but  it  is  impossible  to  say  if  this  will  always  be  the 
case. 

The  adoption  of  the  scale  of  the  gas-thermometer  does 
not  in  any  way  imply  the  obligation  to  use  this  instrument 
actually  in  all  measurements.  Any  thermometer  may 
be  taken,  provided  that  in  the  first  place  its  particular 
scale  has  been  standardized  by  comparing  it  with  that  of 
the  gas-thermometer.  According  to  the  case,  there  will  be 
advantage  in  employing  one  or  another  method ;  practically 
also  one  almost  never  employs  the  gas-thermometer  by 
reason  of  the  difficulties  inherent  in  its  use,  which  result 
principally  from  its  great  dimensions  and  its  fragility. 

For  the  estimation  of  very  high  temperatures  the  gas- 
scale  can  be  used  only  by  an  indirect  extrapolation  in 
terms  of  some  property  of  matter  whose  variation  has 


INTRODUCTION.  5 

been  studied  within  the  range  of  the  gas-scale  attainable 
experimentally  and  which  variation  is  assumed  to  obey 
the  same  law  at  temperatures  beyond  which  control  cannot 
be  had  with  the  gas-thermometer. 

The  gas-scale  has  not  been  experimentally  determined 
above  1150°  C.,  and  extrapolations  to  1600°  C.  may  be  made 
by  means  of  thermocouples  made  of  the  platinum  metals, 
assuming  the  law  connecting  E.M.F.  and  temperature  to 
be  the  same  above  1150°  C.  as  below.  Beyond  1600°  C. 
the  most  infusible  substances  permanently  alter  their 
properties  and  we  are  forced  to  measure  temperature  in 
terms  of  the  radiations  coming  from  heated  bodies  for  the 
reason  that  we  have  not  been  able  to  find  any  other  than 
the  radiating  properties  of  such  excessively  heated  bodies 
whose  variations  can  be  measured  without  destroying 
or  permanently  altering  either  the  substance  used  as 
pyrometer  or  the  substance  examined.  Perhaps  also 
chemical  methods  may  be  employed  eventually. 

It  is  in  the  realm  of  the  laws  of  radiation  and  their  appli- 
cations to  pyrometric  methods  that  some  of  the  most  re- 
cent and  important  advances  in  high  temperature  measure- 
ments have  been  made,  so  that,  with  certain  restrictions 
which  will  be  treated  in  the  chapter  on  the  laws  of  radiation, 
it  is  possible  to  measure  on  a  common  scale  the  tempera- 
tures of  bodies  heated  to  the  highest  attainable  limits. 

It  is  our  purpose,  in  this  introduction,  to  pass  in  review 
rapidly  the  different  pyrometric  methods  (that  is  to  say, 
thermometers  utilizable  at  high  temperatures)  whose 
employment  may  be  advantageous  in  one  or  another  cir- 
cumstance; we  shall  then  describe  more  in  detail  each  of 
them,  and  shall  discuss  the  conditions  for  their  employ- 
ment. But  in  the  first  place  it  is  necessary  to  define 
within  what  limits  the  different  scales  may  be  compared  to 
that  of  the  normal  gas-thermometer;  it  is  the  insufficiency 


6  HIGH  TEMPERATURES. 

of  this  comparison  which  is  still  to-day  the  cause  of  the 
most  important  errors  in  the  measurement  of  high  tem- 
peratures. 

Fixed  Points. — The  standardization  of  the  different 
pyrometers  is  the  most  frequently  made  by  means  of  the 
fixed  points  of  fusion  and  ebullition  which  have  been 
determined  in  the  first  place  by  means  of  the  gas-ther- 
mometer; the  actual  precision  of  the  measurements  of 
high  temperatures  is  entirely  subordinate  to  that  with 
which  these  fixed  points  are  known;  this  precision  was 
for  a  long  time  most  unsatisfactory  because  these  fixed 
points  could  only  be  determined  in  an  indirect  manner 
with  the  gas-thermometer,  and  some  of  them  only  by 
aid  of  processes  of  extrapolation,  always  very  uncertain. 
Recent  researches,  however,  by  various  observers,  in 
which  improved  methods  of  heating  have  been  used,  as 
well  as  greater  purity  of  materials  and  more  carefully 
constructed  and  calibrated  apparatus,  have  led  to  most 
concordant  results,  in  the  determination  of  fixed  points, 
even  by  most  varied  methods. 

Violle  was  the  first  to  make  a  series  of  experiments  of 
considerable  precision,  which  up  to  the  last  few  years 
were  our  only  reliable  data  on  the  question.  In  a  first 
series  of  researches  he  determined  the  specific  heat  of 
platinum  by  direct  comparison  with  the  air-thermometer 
between  the  temperatures  of  500°  and  1200°.  He  made 
use  indirectly  of  the  relation  thus  established  between 
specific  heat  and  temperature  to  determine  by  compari- 
son with  platinum  the  points  of  fusion  of  gold  and  silver; 
then,  by  extrapolation  of  this  same  relation,  the  points  of 
fusion  of  palladium  and  of  platinum. 

^     .  j     Ag  Au  Pd  Pt 

3n 1954°       1045°       1500°       1779° 

Finally,  in  a  second  series  of  experiments,  he  deter- 


INTRODUCTION.  7 

mined  by  direct  comparison  with  the  air-thermometer  the 
boiling-point  of  zinc. 

Boiling-point j  92gn  6 

Bams,  chemist  of  the  United  States  Geological  Survey, 
has  determined  the  boiling-points  of  several  metals  by 
means  of  thermoelectric  couples  standardized  against  the 
air-thermometer. 

Boiling-point j  772o  ^  784o       92go  J£j  931o 

Mean 778°  928°. 5 

Callendar  and  Griffiths,  by  means  of  a  platinum  resist- 
ance-thermometer calibrated  up  to  500°  by  comparison 
with  the  air-thermometer,  have  determined  the  following 
points  of  fusion  and  ebullition: 

.  j     Sn  Bi  Cd  Pb  Zn 

* uslon \  232°        270°      322°       329°       421° 

Boiling-point       j  Aniline   Naphthaline   Benzophenone     Mercury     Sulphur 
under  760  mm.     |184°.l      217°. 8  305°. 8          356°. 7     444°. 5 

These  last  figures  may  be  compared  with  Regnault's,  and 
Crafts'  previous  determinations: 

Naphthaline     Benzophenone         Mercury         Sulphur 
218°  306°.  1  357°  445° 

Heycock  and  Neville,  employing  the  same  method,  but 
with  extrapolation  of  the  law  of  resistance  for  platinum 
established  only  up  to  450°,  have  determined  the  follow- 
ing points  of  fusion: 

Sn  Zn       (99M5%)         Sb  (99%)  Ag  AU  ^ 

232°      419°      633°      629°.5      654°.5      960°.5       1062°       1080°.  5 

At  the  Physikalische  Reichsanstalt  in  Berlin,  the  ques- 
tion of  establishing  a  temperature  scale  has  received 
deserved  attention.  In  the  early  nineties  Holborn  and 


8  HIGH    TEMPERATURES. 

Wien,  using  a  thermocouple  calibrated  in  terms  of  a  porce- 
lain-bulb nitrogen- thermometer,  found  the  fusing  points : 

^    .  j  Ag  AU  Pd  pt 

on \  970°         1072°         1580°        1780° 

With  the  possible  exception  of  the  Pt  point  these 
results  were  subsequently  found  to  be  all  high  by  Holborn 
and  Day,  who  worked  with  a  platinum-iridium  bulb  nitro- 
gen-thermometer and  thermocouple,  employing  electric 
heating,  two  improvements  that  greatly  increased  the 
accuracy,  and  they  unquestionably  have  obtained  the 
results  meriting  the  greatest  confidence.  Among  others 
they  determined  the  following: 

.         (   Cd     Zn     Sb     Al     Ag    Au    Cu 
on (321°. 7  419°  630°. 5  657°. 5  961°. 5  1064°  1084° 

Mr.  Daniel  Berthelot,  in  a  series  of  most  skilfully  exe- 
cuted investigations  extending  over  several  years,  has 
recently  calibrated  thermocouples  by  comparison  with  a 
special  form  of  gas-thermometer,  making  use  of  the  varia- 
tion of  the  index  of  refraction  with  density.  He  has  in 
this  way  found  the  points: 

f    Ag  Au 

Fusion \962°       1064° 

™     ,,.,.  Se  Cd  Zn 

:ion 690°        778°        918° 

Besides  these  primary  measurements  there  are  some 
very  important  secondary  determinations,  which  will  be 
discussed  later.  From  all  the  results  at  hand  we  may 
conclude  that  the  fixed  points  possessing  the  greatest 
reliability  for  the  indirect  standardization  of  the  various 
thermometric  scales  and  thus  for  the  calibration  of  pyrom- 
eters are  the  following: 

.  j     Sn        Zn          Sb          Al         Ag  Au  Pt  Ir 

on }  232°     419°     630°    657°    961°     1065°     1780°    2250" 

-,,     ...  .  (  Naphthaline          S  Cd  Zn 

Ebullition |      217° .  9      444° .  6      778°      925° 


INTRODUCTION.  9 

We  may  consider  the  temperature  scale  as  known  with 
an  accuracy  better  than: 

0°.5 between  200°  and  500° C. 

3       "        500      "     800 

5       "        800      "    1100 

25       "      1100      "    1600 

50        above    1600 

A  more  detailed  discussion  of  the  determination  of 
fixed  points  and  their  reliability  and  ease  of  reproduction 
will  be  found  in  Chapter  XIII  on  Standardization. 

Pyrometers. — There  have  been  a  great  number  of 
pyrometric  methods  proposed,  among  which  we  shall 
dwell  only  upon  those  which  have  had  considerable  use 
or  promise  to  be  useful. 

Gas-pyrometer  (Pouillet,  Becquerel,  Sainte-Claire-Deville, 
Barus,  Chappuis,  Holborn,  Callendar). — Utilizes  the  meas- 
urement of  change  in  pressure  of  a  gaseous  mass  kept  at 
constant  volume.  Its  great  volume  and  its  fragility  ren- 
der it  unsuitable  for  ordinary  measurements ;  it  serves  only 
to  give  the  definition  of  temperature  and  should  only  be 
used  to  standardize  other  pyrometers. 

Calorimetric  Pyrometer  (Regnault,  Violle,  Le  Chatelier, 
Siemens). — Utilizes  the  total  heat  of  metals  (platinum  in 
the  laboratory  and  nickel  in  industrial  works).  Is  to  be 
recommended  for  intermittent  researches  in  industrial 
establishments  because  its  employment  demands  almost 
no  apprenticeship  and  because  the  cost  of  installation  is 
not  great. 

Radiation-pyrometer  (Rosetti,  Langley,  Boys,  Rubens, 
Fery). — Utilizes  the  total  heat  radiated  by  warm  bodies. 
Its  indications  are  influenced  by  the  variable  emissive 
power  of  the  different  substances.  Convenient  for  the 
evaluation  of  very  high  temperatures  which  no  thermo- 
metric  substance  can  withstand  (electric  arc,  sun). 


10  HIGH  TEMPERATURES. 

Optical  Pyrometer  (Becquerel,  Le  Chatelier,  Winner,  Hol- 
born-Kurlbaum,  Morse). — Utilizes  either  the  photometric 
measurement  of  radiation  of  a  given  wave-length  of  a 
definite  portion  of  *the  visible  spectrum,  or  the  disappear- 
ance of  a  bright  filament  against  an  incandescent  back- 
ground. Its  indications,  as  in  the  preceding  case,  are 
influenced  by  variations  in  emissive  power.  The  inter- 
vention of  the  eye  aids  greatly  the  observations,  but  dimin- 
ishes notably  their  precision.  This  method  is  mainly  em- 
ployed in  industrial  works  for  the  determination  of  the 
temperatures  of  bodies  difficult  of  access — for  example, 
of  bodies  hi  movement  (the  casting  of  a  metal,  the  hot 
metal  passing  to  the  rolling-mill). 

Electric-resistance  Pyrometer  (Siemens,  Callendar).— 
Utilizes  the  variations  of  electric  resistance  of  metals 
(platinum)  with  the  temperature.  This  method  permits 
of  very  precise  measurements,  but  requires  the  employ- 
ment of  fragile  and  cumbersome  apparatus.  It  will  merit 
the  preference  for  very  precise  investigations  in  laboratories 
when  we  have  a  satisfactory  determination  of  the  variation ' 
of  resistance  of  platinum  in  terms  of  the  normal  gas- 
thermometer.  As  a  secondary  instrument  for  the  repro- 
duction of  a  uniform  temperature  scale  throughout  the 
range  in  which  the  platinum  resistance  thermometer  can 
be  used,  it  is  unsurpassed  in  precision  and  sensibility.  It 
is  also  now  constructed  in  convenient  form  for  industrial 
use. 

Thermoelectric  Pyrometer  (Becquerel,  Barus,  Le  Chate- 
lier).— Utilizes  the  measure  of  electromotive  forces  devel- 
oped by  the  difference  in  temperature  of  two  similar 
thermoelectric  junctions  opposed  one  to  the  other.  In 
employing  for  this  measurement  a  Deprez-d'Arsonval  gal- 
vanometer with  movable  coil,  one  has  an  apparatus  easy 
to  handle  and  of  a  precision  amply  sufficient  considering 


INTRODUCTION.  11 

the  actual  state  of  the  means  of  standardization  at  our 
disposal  in  terms  of  the  normal  scale  of  temperature.  This 
pyrometer,  which  has  been  used  for  a  good  many  years  in 
scientific  laboratories,  is  rapidly  spreading  into  general 
industrial  use,  where  it  renders  most  valuable  service. 

Contraction-pyrometer  (Wedgwood). — Utilizes  the  per- 
manent contraction  that  clayey  materials  take  up  when 
submitted  to  temperatures  more  or  less  high.  It  is  em- 
ployed to-day  only  in  a  few  pottery  works. 

Fusible  Cones  (Seger). — Utilize  the  unequal  fusibility 
of  earthenware  blocks  of  varied  composition.  Give  only 
discontinuous  indications.  Such  blocks  studied  by  Seger 
are  spaced  so  as  to  have  fusing-points  distant  about  20°. 
In  general  use  in  pottery  works  and  in  some  similar  in- 
dustries. 

There  are  a  number  of  other  pyrometers  which  have  been 
found  suitable  in  special  cases  or  which  for  one  reason  or 
another  have  been  found  convenient  in  some  particular 
line -of  work.  Some  of  these  we  shall  mention,  among 
them  being  the  meldometer  (Joly),  interesting  to  the 
chemist  or  metallurgist  for  deterrnining  fusing  tempera- 
tures of  minute  specimens;  the  various  industrial  instru- 
ments based  on  the  relative  expansion  of  metals  or  of  a 
metal  and  graphite  used  in  air-blasts  and  metal  baths ;  and 
finally  pyrometers  based  on  the  flow  of  air  or  vapor 
(Hobson,  Uhling-Steinbart,  Job). 


CHAPTER  I. 
NORMAL  SCALE  OF  TEMPERATURES. 

WE  have  seen  that  temperature  is  not  a  measurable 
quantity;  it  is  merely  comparable  with  respect  to  a  scale 
arbitrarily  chosen. 

The  normal  scale  is  the  thermodynamic  scale;  but  as  it 
is  impossible  to  realize  rigorously  this  scale,  it  is  necessary 
to  have  a  practical  one.  In  the  same  way  that,  besides  the 
theoretical  definition  of  the  meter,  there  is  a  practical 
standard,  a  certain  meter  kept  at  the  Bureau  International 
des  Poids  et  Mesures,  there  exists,  besides  the  normal 
scale  of  temperatures,  a  practical'  scale  which  is  a  certain 
gas-thermometer  which  we  are  going  to  study. 

Laws  of  Mariotte  and  Gay-Lussac.  —  The  laws  of  Mario  tte 
and  Gay-Lussac  are  the  basis  for  the  use  of  the  dilatation 
of  gases  for  the  determination  of  temperatures.  These 
two  laws  may  be  written 


the  temperatures  being  measured  with  the  mercury- 
thermometer.  a  is  a  numerical  coefficient,  the  same  for 
all  gases,  at  least  to  a  first  approximation,  and  its  value  is 


12 


NORMAL  SCALE  OF  TEMPERATURES.  13 

when  it  is  agreed  that  the  interval  between  the  tempera- 
tures of  melting  ice  and  boiling  water  is  100°. 

But  instead  of  considering  the  formula  (1)  as  the  ex- 
pression of  an  experimental  law  joining  the  product  pv  to 
the  temperature  defined  by  the  mercury-thermometer,  we 
may  require  of  experiment  merely  the  law  of  Mariotte  and 
write  a  priori  the  formula  in  question,  giving  a  new  defini- 
tion of  temperature  approximating  that  of  the  mercury- 
thermometer.  This  new  scale  has  the  advantage  that  it 
adapts  itself  to  the  study  of  very  much  higher  tempera- 
tures. The  use  of  this  process  suggested  by  Pouillet  was 
carefully  studied  by  Regnault. 

The  expression  for  the  laws  of  Mariotte  and  Gay-Lussac 
can  be  put  in  the  form 


(2) 


by  calling  n  the  number  of  units  of  quantity  (this  unit 
may  be  either  the  molecular  weight  or  the  gramme)  ;  R 
the  value  of  the  expression 


for  unit  quantity  of  matter  taken  at  the  temperature  of 
melting  ice  and  under  atmospheric  pressure. 

Gas-thermometers.  —  The  equivalent  expressions  (1)  and 
(2)  which  arbitrarily  by  convention  give  the  definition  of 
temperature,  can  be  utilized,  from  the  experimental  point 
of  view,  in  various  ways  for  the  realization  of  the  normal 
thermometer. 

1.  Constant-volume  Thermometer.  —  In  the  thermometer 
designated  by  this  name,  the  volume  and  the  mass  are  kept 
invariable. 


14  HIGH  TEMPERATURES. 

The  expression  (2)  then  gives  between  the  two  tempera- 
tures t  and  t0  the  relation 


Po 
from  which 


(3) 


2.  Constant-pressure  Thermometer.  —  In  this  case  the 
pressure  and  the  volume  of  the  heated  mass  remain  con- 
stant, but  the  mass  is  variable  ;  a  part  of  the  gas  leaves  the 
reservoir.  The  expression  (2)  then  gives 


= 

* 

a 
from  which 


It  would  be  much  more  logical,  instead  of  the  classic  ex- 
pressions constant-volume  thermometer  or  constant-pres- 
sure thermometer,  to  say  thermometer  of  variable  pressure, 
thermometer  of  variable  mass,  which  describe  much  more 
exactly  the  manner  of  their  action. 

3.  Thermometer  of  Variable  Pressure  and  Mass.  —  The 
action  of  this  apparatus  combines  those  of  the  two  pre- 
ceding types.  A  part  of  the  gas  leaves  the  reservoir,  and 
the  pressure  is  not  kept  constant.  The  expression  (2) 
gives 

l+i 

£.  —  !L   a 

Po~'n~o'L  +  t' 
a      * 


NORMAL  SCALE  OF  TEMPERATURES.  15 

from  which 


4.  Volumetric  Thermometer.  —  There  exists  a  fourth 
method  of  the  use  of  the  gas-thermometer  which  was  sug- 
gested by  Ed.  Becquerel,  and  presents,  as  we  shall  see 
later,  a  particular  interest  for  the  evaluation  of  high  tem- 
peratures. We  keep  the  name  for  it  given  by  its  inventor. 
The  determination  of  the  temperature  is  obtained  by  two 
measurements  made  at  the  same  temperature,  and  not  as 
in  the  preceding  methods  by  two  measurements  made  at 
two  different  temperatures  one  of  which  is  supposed 
known.  The  mass  contained  in  the  reservoir  is  varied, 
and  the  ensuing  change  of  pressure  is  observed.  The 
expression  (2)  gives 


from  which 


or 


This  necessitates  a  preliminary  determination  of  the  con- 
stant R. 

In  the  particular  case  in  which  p'=0,  which  supposes 
that  a  complete  vacuum  is  obtained,  the  preceding  relation 
becomes  simpler  and  is 

<--*-+£.£  .......    (7) 

a     n    R 


16 


HIGH  TEMPERATURES. 


The  definitions  of  temperature  given  by  these  different 
thermometers  would  be  equivalent  among  themselves  and 
with  that  of  the  mercury-thermometer  if  the  laws  of 
Mariotte  and  Gay-Lussac  were  rigorously  exact,  as  used  to 
be  held.  The  only  advantage  of  the  gas-thermometer  in 
that  case  would  be  to  extend  to  high  temperatures  the 
scale  of  the  mercury-thermometer.  In  this  way  it  was 
employed  by  Pouillet,  Becquerel,  Sainte-Claire-Deville. 

Experiments  of  Regnault. — The  very  precise  experiments 
of  Regnault  caused  a  modification  in  the  then  admitted 
ideas  concerning  the  mercury-thermometer  as  well  as  the 
gas-thermometer,  and  have  led  to  the  definite  adoption  of 
a  normal  gas-thermometer. 

In  the  first  place  these  experiments  established  that 
different  mercury-thermometers  are  not  comparable  among 
themselves  on  account  of  the  unequal  dilatation  of  the 
differing  glass  employed  in  their  construction.  Thus  they 
cannot  give  an  invariable  scale  for  the  determination  of 
temperature.  In  comparing  them  from  0°  to  100°  they 
do  not  present  between  these  extreme  temperatures  very 
great  differences,  0°.30  as  a  maximum,  but  at  tempera- 
tures above  100°  these  differences  may  become  considerable 
and  reach  10.° 


Constant-  vol. 

Mercury-thermometer  in 

Air-thermom- 

eter, 
P0=760. 

Crystal. 

White  Glass. 

Green  Glass. 

Bohemian 
Glass. 

100° 

+  o°.oo 

+o°.oo 

+o°.oo 

+o°.oo 

150 

+  0  .40 

-0  .20 

+  0   .30 

+  0   .15 

200 

+   1  .25 

-0  .30 

+  0  .80 

+  0  .50 

250 

+  3  .00 

+  0  .05 

+  1  .85 

+  1  .44 

300 

+  5  .72 

+  1  .08 

+  3  .50 

350 

+  10  .50 

+  4  .00 

NORMAL  SCALE  OF  TEMPERATURES.  17 

The  numbers  figuring  in  this  table  indicate  the  quan- 
tities by  which  it  is  necessary  to  increase  or  diminish  the 
temperatures  given  by  the  air-thermometer  in  order  to 
have  them  correspond  with  those  which  were  observed  with 
the  different  mercury-thermometers. 

It  was  thus  impossible  to  define  the  practical  scale  of 
temperatures  in  terms  of  the  mercury-thermometer.  The 
use  of  the  gas-thermometer  became  necessary.  But 
Regnault  recognized  that  it  was  not  possible  to  take  a 
single  coefficient  of  dilatation  a,  independent  of  the  nature 
of  the  gas,  of  its  pressure,  and  of  the  mode  of  dilatation 
utilized.  The  coefficient  of  expansion  at  constant  volume 
(a)  and  the  coefficient  of  expansion  at  constant  pressure 
(/?)  are  not  identical.  This  follows  from  the  fact  that  the 
law  of  Mario tte  is  not  rigorously  exact;  we  have  in  reality 

pv=pQv0+e, 

e  being  a  very  small  quantity,  but  not  zero. 

The  experiments  of  Regnault  permitted  him  not  only 
to  detect  but  to  measure  this  variation  of  the  coefficient 
of  expansion.  Here  are,  for  example,  the  results  which 
he  found  for  air  between  0°  and  100°: 

Volume  Constant.  Pressure  Constant. 


Pressure. 


266 

0.003656 

273.6 

760 

0.003671 

272.4 

760 

3655 

272.8 

2525 

3694 

270.7 

1692 

3689 

271 

2620 

3696 

270.4 

3655 

3709 

269.5 

For  air  at  4°. 5  Rankine  obtains,  from  the  experiments 
of  Regnault,  the  formula 

pv=p0v0+Q.OQ8l63^ —  '  I™, 
CD  being  the  atmospheric  pressure. 


18 


HIGH  TEMPERATURES. 


These  coefficients  vary  also  from  one  gas  to  another,  as 
is  shown  by  the  following  table,  taken  also  from  Regnault's 
experiments : 

MEAN  COEFFICIENT  BETWEEN  0°  AND  100°. 

Volume  Constant.  Pressure  Constant. 


Pressure, 
mm. 


760 
3655 

760 


760 
760 

760 
3589 

760 


Pressure. 


0.003665 
3708 

3667 


3667 
3668 

3688 
3860 

3845 


AIR. 

272.8  760 

269.5  2620 

HYDROGEN. 

272.7  760 

2545 

CARBON   MONOXIDE. 

272.7  760 

NITROGEN. 

272.6 

CARBONIC   ACID. 

271.2  760 

259  2520 

SULPHUROUS   ACID. 

259.5  760 

980 


0.003671 
3696 

36613 
36616 


272.4 
270.4 

273.1 
273.2 


3669      272.5 


3710 
3845 

3902 
3980 


296.5 
259.5 

253.0 
251.3 


These  experiments  show  that  the  easily  liquefiable  gases 
have  coefficients  quite  different  from  those  of  the  per- 
manent gases. 

For  the  permanent  gases  the  coefficients  for  constant 
volume  differ  much  less  among  themselves  than  those  for 
constant  pressure;  for  the  former  the  extreme  deviation 
does  not  exceed  T7Vo  J  f°r  the  latter  it  is  three  times  as 
great.  Setting  aside)  air,  which  is  a  mixture  and  which 
contains  more  easily  liquefiable  oxygen,  the  coefficients  for 
constant  volume  of  H2,  N2,  and  CO  are  identical. 


NORMAL  SCALE  OF   TEMPERATURES. 


19 


Finally,  for  hydrogen  the  coefficient  of  expansion  does 
not  vary  with  the  pressure. 

The  inequality  of  the  coefficients  of  expansion,  however^ 
does  not  prevent  us  from  taking  any  gas  whatever  to 
define  the  scale  of  temperature,  provided  we  apply  to  it 
the  proper  coefficient  determined  by  experiment  between 
0°  and  100°.  The  scales  are  identical,  if  the  coefficients 
of  expansion  do  not  vary  with  the  temperature.  This  is 
the  conclusion  to  which  Regnault  came  from  a  comparison 
of  thermometers  at  constant  volume,  differing  by  their 
initial  pressure  or  the  nature  of  the  gas.  Here  are  the 
results  obtained,  starting  from  the  fixed  points  0°  and 
100°,  by  the  aid  of  the  following  formulae: 

pv=nRT, 

pQv=nRT0, 

pmv=nRTlw, 


ICO 


AIR-THERMOMETER. 


Po=751  mm. 

Po  =  I486  mm. 

Degrees. 
156.18 

Degrees. 
156.19 

259.50 

259.41 

324.33 

324.20 

PRESSURE  =760   MILLIMETERS. 


Air- 
thermometer. 

Hydrogen- 
thermometer. 

Air- 
thermometer. 

(XV 
thermometer. 

Degrees. 

141.75 

Degrees. 
141.91 

Degrees. 
159.78 

Degrees. 
160.00 

228.87 

228.88 

267.35 

267.45 

325.40 

325.21 

322.8 

322.9 

20  HIGH   TEMPERATURES. 

The  deviations  do  not  exceed  0°.2,  a  value  that  Regnault 
estimated  not  to  exceed  the  limits  of  error  of  his  experi- 
ments; he  concluded  from  this  that  one  gas  may  be  used 
as  well  as  another,  and  he  took  air  for  the  normal  ther- 
mometer. 

Nevertheless  his  experiments  on  sulphurous  acid  had 
shown  a  very  marked  variation  of  the  coefficient  of  expan- 
sion of  this  gas  with  the  temperature.  The  following 
table  gives  the  mean  coefficient  at  constant  volume  be- 
tween 0°  and  t°: 

t  a. 

98.0 0.0038251 

102.45 38225 

185.42 37999 

257.17 37923 

299.90 37913 

310.31 37893 

By  analogy  it  is  permissible  to  suppose  that  a  similar 
effect  should  take  place  with  -the  other  gases;  but  the 
differences  were  then  too  small,  and  the  degree  of  precision 
of  the  methods  of  Regnault  insufficient  to  detect  it. 

Results  Obtained  by  Chappuis. — This  effect  has  been 
demonstrated  by  experiments  of  very  great  precision 
made  at  the  Bureau  International  des  Poids  et  Mesures, 
at  Sevres.  Chappuis  has  found,  between  0°  and  100°, 
systematic  deviations  between  thermometers  of  hydrogen, 
nitrogen,  and  carbonic  acid,  filled  at  0°  under  a  pressure 
of  1000  mm.  of  mercury. 

Hydrogen  Ther.  N  Ther.— H  Ther.  N  Ther.— CO2  Ther. 

-   15°  -0°.016  -0°.094 

000 

+  25  +0  .011  +0  .050 

+  50  +0  .009  +0.  059 

+  75  +0  .011  +0  .038 

+  100  0  0 


Of    THE 

UNIVERSITY 

Or 


BMAL  SCALE  OF  TEMPERATURES. 


21 


In  this  table,  taking  as  definition  of  the  temperature 
the  hydrogen-thermometer  at  constant  volume,  the  num- 
bers in  the  last  two  columns  indicate  the  deviations 
observed  with  the  thermometers  of  nitrogen  and  carbonic 
acid;  it  is  certain  that  these  deviations  are  systematic. 
These  results  allow  of.  the  determination  of  the  mean 
coefficients  of  expansion: 


t  a  (Hydrogen) 

0° 

100°         0.00366254 


a  (Nitrogen). 

0.00367689 

367466 


(Carbonic  Acid). 
0.00373538 
372477 


Thus  the  coefficients  decrease  with  rise  of  temperature, 
while  remaining  higher  than  that  of  hydrogen,  to  which 
they  tend  to  approach.  The  more  recent  work  of  Chap- 
puis  and  Harker  and  others  in  the  establishment  of  a 
normal  scale  of  temperatures  for  high  temperatures  will 
be  discussed  in  the  following  sections. 

In  the  interval  0° — 100°,  the  values  given  above,  calcu- 
lated from  Chappuis'  data  of  1888,  may  not  be  absolutely 


DIFFERENCE    BETWEEN    SCALES    OF  NITROGEN-  AND 
HYDROGEN-  THERMOMETERS. 


—tii.  vol.  =  const., 


100  ems. 


Temp. 
Cent. 

Callendar. 
1903. 

Chappuis. 
1902. 

Rose-Innes. 
1901. 

Lehfeldt. 
1898. 

+  20 

+  .006 

+  .005 

+  .002 

+  .011 

+  40 

+  .009 

+  .008 

+  .002 

+  .017 

+  50 

+  .009 

+  .010 

+  .002 

+  .019 

+  60 

+  .008 

+  .009 

+  .002 

+  .019 

+  80 

+  .005 

+  .004 

+  .001 

+  .015 

22  HIGH  TEMPERATURES. 

exact,  but  they  are  probably  very  nearly  correct.  Some 
of  the  later  results  are  given  below;  those  marked  Cal- 
lendar  are  calculated  by  him  from  the  data  of  Kelvin  and 
Joule  using  a  modified  formula;  Chappuis'  results  are  from 
his  latest  determinations  (1902)  while  those  of  Lehrfeldt 
and  Rose-Innes  are  calculations  involving  special  ther- 
modynamical  assumptions. 

Normal  Scale  of  Temperatures. — It  results  from  these 
experiments  that  the  different  scales  furnished  by  the 
various  gas-thermometers  are  not  rigorously  identical;  the 
deviations  between  0°  and  100°  are  very  small,  but  their 
existence  is  certain.  It  becomes  necessary,  therefore,  in 
order  to  have  a  scale  of  temperature  rigorously  defined,  to 
make  a  choice' of  the  nature  of  the  gas,  of  its  manner  of 
dilatation,  and  of  its  initial  pressure. 

The  normal  thermometer  selected  by  the  Bureau  Inter- 
national des  Poids  et  Mesures  to  define  the  practical  scale 
of  temperatures,  and  everywhere  adopted  to-day,  is  the 
hydrogen  thermometer,  operated  at  constant  volume  and 
filled  with  gas  at  1000  millimeters  of  mercury  at  the  tem- 
perature of  melting  ice. 

For  high  temperatures  this  definition  is  inadmissible, 
because  we  would  reach  such  pressures  that  the  apparatus 
could  not  withstand.  The  use  of  the  method  at  constant 
volume,  that  is  to  say,  at  invariable  mass,  is  besides  bad 
on  account  of  the  permeability  of  the  coverings  at  high 
temperatures.  It  would  be  of  great  advantage  to  be  able 
to  employ  a  gas  other  than  hydrogen  and  operate  the 
thermometer  at  variable  mass. 

In  the  actual  state  of  experimentation  at  high  tempera- 
tures, it  is  impossible  to  have  results  exact  to  about  1° 
and  indeed,  practically,  we  are  far  from  arriving  at  this 
precision.  It  is  very  likely  that  we  can,  under  these  con- 
ditions, employ  indifferently  for  the  construction  of  the 


NORMAL  SCALE  OF  TEMPERATURES.  23 

normal  thermometer  any  permanent  gas  whatsoever. 
According  to  the  preceding  experiments,  all  the  gases 
would  have  a  dilatation  slightly  greater  than  that  for 
hydrogen,  and  their  coefficient  of  expansion,  which  de- 
creases with  rise  of  temperature,  would  approach  that 
for  hydrogen.  For  determining  experimentally  the  error 
possible  with  a  normal  thermometer  thus  modified,  we 
possess  actually  but  little  data. 

Crafts  has  compared  in  the  neighborhood  of  1500°  the 
expansion  at  constant  pressure  of  nitrogen  and  carbonic 
acid,  and  found  for  this  latter  the  mean  coefficient  0.00368 
in  assuming  0.00367  for  nitrogen. 

The  experiments  were  made  by  displacing  in  a  Meyer's 
tube  nitrogen  by  carbonic  acid,  or  carbonic  acid  by  nitro- 
gen. 

10  cc.  N2  displace  10  cc.  CO2  displace 

10.03ofCO3  9.95ofNa 

10.01  9.91 

10.00  9.98 

10.03  9.93 
9.95 
10.09                          Mean  9.94 

Mean  10.02 

The  two  measurements  give  positive  and  negative  differ- 
ences of  the  same  order  of  magnitude;  but  it  should  be 
noticed  that  the  observed  deviation  (-j^-jr  on  an  average) 
hardly  exceeds  the  possible  error  of  observation.  How- 
ever it  may  be,  carbonic  acid,  which  differs  much  from 
the  permanent  gases  at  ordinary  temperatures,  no  longer 
so  differs  in  an  appreciable  degree  at  1500°. 

Violle  has  made  some  comparative  measurements  on 
the  air-pyrometer  used  at  constant  pressure  and  constant 


24  HIGH   TEMPERATURES. 

volume  in  his  determinations  of  the  specific  heat  of  plati- 
num. 

Vol.  Constant.  Press  Constant.  Difference. 

1171°  1165°  6° 

1169  1166  3 

1195  1192  3 

There  was  on  an  average  a  deviation  of  only  4°  between 
the  two  modes  of  observation,  and  the  greater  part  of  this 
deviation  should  be  laid  to  accidental  variations  of  the 
gaseous  mass  resulting  from  the  permeability  of  the  cover- 
ings. 

Chappuis  has  made  an  exhaustive  experimental  study 
of  the  divergences  of  gases  from  the  normal  scale,  and  he 
finds  that  the  coefficient  of  nitrogen  (at  const,  vol.)  gradu- 
ally diminishes  as  above  stated  (p.  21),  but  that  at  about 
75°  C.  it  reaches  a  limiting  value  equal  to 

aum  =0.00367380 

and  it  may  be  assumed  that  above  this  temperature  the 
gas  is  in  a  perfect  state. 

The  mean  coefficient  at  constant  volume  for  this  gas 
between  0°  and.  100°  is 

«o- 100  =0.00367466 

and  the  limiting  value  for  an  initial  pressure  P0=0  is 
aPo=Q  =0.0036613. 

This  follows  from  the  divergence  that  Chappuis  and 
Harker  found  for  the  constant-volume  nitrogen-ther- 
mometer from  the  normal  scale  of  temperatures,  in  terms 
of  the  initial  pressure;  their  experiments  gave 

-5-  =  1.32  •  10~8  per  mm.  change  in  pressure, 


NORMAL  SCALE  OF  TEMPERATURES.  25 

Such  a  normal  scale  of  temperature  for  the  nitrogen-ther- 
mometer is  given  by  finding  the  coefficient  a,  at  0°  C.  for 
a  pressure.  P0'  which  the  gas  would  have  supposing  it 
to  remain  perfect  in  the  range  0—100.  If  P0  =  100  cm., 
P100  =  136.7466  cm.,  whence  P0'  =  100.0086  and  a  = 

,°' = 0.00367348  if  aUm  =0.00367330  as  stated  above. 

Nitrogen  at  constant  pressure  gives 

/?/? 

-/•=  1. 19  •  10- 8  per  mm. 

dp 

and  A^  =  0.0036612. 

The  divergences  from  the  normal  scale  in  this  case  are 
about  double  those  at  constant  volume,  and  the  diver- 
gences between  the  unconnected  scale  and  the  theoretical 
scale  of  the  constant-volume  thermometer  whose  constants 
are  given  above  and  which  represents  the  normal  scale 
of  temperatures,  are  proportional  to  the  temperature 
measured  from  100°  and  have  the  following  values: 

At   100° 0°.000 

200 023 

300 047 

400 070 

These  deviations  are  evidently  very  slight  and  are 
entirely  negligible  within  this  range  for  practically  all 
pyrometric  uses.  We  shall  see,  however,  that  at  1000° 
this  correction  may  assume  a  certain  importance. 

For  hydrogen,  the  limiting  values  given  by  D.  Berthe- 
lot  are: 

aiim  =0.0036625, 
Aim  =0.0036624, 

and  the  deviations  of  this  gas  from  the  normal  scale  are 
immaterial. 


26  HIGH   TEMPERATURES. 

The  experiments  of  Chappuis  and  Harker  were  carried 
out  at  the  International  Bureau  of  Weights  and  Measures 
and  included  a  comparison  of  the  platinum-resistance  and 
nitrogen-thermometers  up  to  500°  C.  and  a  determination 
of  the  sulphur  boiling-point,  to  which  questions  we  shall 
return. 

We  can  then  affirm  that,  in  employing  any  permanent 
gas  with  any  mode  of  dilatation,  we  shall  not  differ  cer- 
tainly by  more  than  5°  at  1000°  from  the  temperature  of 
the  normal  scale,  and  in  reality  the  deviation  will  be 
without  doubt  much  less,  and  should  not  reach  1°. 

Theoretically  it  would  be  preferable  to  use  hydrogen 
under  reduced  pressure,  which  would  certainly  not  give 
deviations  of  1°  from  the  normal  scale  ;  but  there  is  always 
the  danger  of  the  passage  of  this  gas  through  the  cover- 
ings, and  of  its  combustion  by  oxygen  or  oxides. 

Practically  it  would  be  better  to  take  nitrogen,  whose 
expansion  deviates  little  from  that  of  hydrogen,  less  than 
the  deviation  of  air.  Callendar  has  suggested  the  use 
of  helium  or  one  of  the  other  newly  discovered  inert, 
mqnatomic  gases,  as  they  diverge  less  than  nitrogen  from 
the  hydrogen  scale,  cannot  dissociate  and  do  not  pass 
through  metals. 

For  high  temperatures  the  normal  thermometer  -will 
be,  then,  one  of  nitrogen  or  other  inert  gas. 

Thermodynamic  Scale.  —  It  is  defined,  in  terms  of  Car- 
not's  principle  applied  to  a  reversible  cycle  working 
between  two  sources  at  constant  temperatures,  by  the 
relation 


1.  Approximate    Expression.—  Consider    Carnot's    cycle 
formed,  as  is  well  known,  of  two  isotherms  and  two  adia- 


NORMAL  SCALE  OF  TEMPERATURES.  27 

batics,  and  let  us  seek  the  quantity  of  heat  absorbed  fol- 
lowing the  isotherm  7\. 
From  Joule's  experiments  we  have  approximately 

Q,=Afpdv. 
The  laws  of  Mariotte  and  Gay-Lussac  give 


where  t  is  the  temperature  of  the  gas-thermometer;  then, 


p     a 


Similarly, 

Q0 
Equation  (1)  becomes 


But  the  experiments  on  adiabatic  expansion  give 

pvr=  const., 

and  combining  with  the  laws  of  Mariotte  and  Gay-Lussac, 
pr-i.t~r  =  const. 


28  mail  TEMPERATURES. 

Consequently—  depends  only  on  the  ratio  -*,  which  is  the 

Po  to 

same  the  whole  length  of  the  two  isotherms.     Thus 


or 


ft'      ft'" 


ft'7      ?«"' 


Equation  (2)  then  takes  the  very  simple  form 

1 

7\_g+\ 


that  is  to  say,  the  ratio  of  the  absolute  thermodynamic  tem- 
peratures is  equal  to  the  ratio  of  the  absolute  temperatures 
of  the  gas-thermometer;  and  if  in  the  two  scales  it  is  agreed 
to  take  equal  to  100  the  interval  comprised  between  the 
temperatures  of  melting  ice  and  the  vapor  of  boiling  water, 
we  have,  at  any  temperature,  the  equality 

T=-+t. 
a 

But  this  is  only  a  first  approximation,  for  we  have  em- 
ployed relations  that  are  but  roughly  so:  the  laws  of 
Joule,  Mariotte,  and  Gay-Lussac. 

2.  Reconsider  the  problem  by  a  more  exact  method. 

Since  T  differs  very  little  from  -,  and  since  the  laws 


NORMAL  SCALE  OF  TEMPERATURES.  29 

of  Mariotte  and  Gay-Lussac  are  nearly  true,  we  place,  fol- 
lowing a  method  of  calculation  indicated  by  Callendar, 


(f>  being  a  very  small  function  of  p  and  of  T  (thermo- 
dynamic  temperature). 

We  have  then,  between  the  temperature  of  the  gas- 
thermometer  and  the  thermodynamic  temperature,  the 
relation 


which  will  permit  of  passing  from  one  scale  of  tempera- 
ture to  the  other  if  we  know  the  corresponding  value 
of  <£. 

Consider,  as  before,  Carnot's  cycle,  and  let  us  deter- 
mine the  heat  of  isothermal  expansion  in  a  more  exact 
manner,  by  utilizing  the  experiments  of  Joule  and  Thom- 
son on  the  expansion  through  a  porous  plug,  and  those 
of  Regnault  on  the  deviations  from  Mario  tte's  law. 

We  write  for  this  that  the  changes  in  energy  between 
two  given  isothermal  states  are  the  same,  either  for  the 
reversible  expansion  or  for  the  expansion  of  Joule  and 
Thomson. 


Q.-A 

pi'  Po' 

e  being  the  very  feeble  change  in  heat  of  the  gas  accom- 
panying its  passage  through  the  porous  plug,  in  the 
experiment  of  Joule  and  Thomson.  We  get  from  this 

Q^=A  I       vdp-\-    I  ~C--dp  (at    constant  temperature),  (3) 
JPI'  J    &P 


30  HIGH  TEMPEtiATUttES. 

for 

d(pv)=pdv  +  vdp. 
The  relation 

pv=RT(l-<f>) 

gives  for  the  value  of  v 

HI  /H|      rx 
«"=—  (l-$i 

which,  substituted  in  equation  (3),  leads  to 


Similarly,  we  have 


If  we  introduce  these  values  in  the  expression  for 
Carnot's  cycle,  after  division  by  Tv  and  T0  we  should  find 
an  identity: 


p 
The  law  of  adiabatic  expansion  gives 


In  order,  then,  that  the  expression  reduce  to  an  identity 
it  is  necessary  that 

1    ds      .  D<£  ,     de          11 

-=AR<    or    ^' 


Referring  to  the  experiments  on  air  of  Joule  and  Thom- 
son, we  have 

*-0.001173A  @', 


NORMAL  SCALE  OF  TEMPERATURES. 


31 


p0  being  the  atmospheric  pressure,  and  T0  the  tempera- 
ture of  melting  ice. 

This  is  still  an  approximate  result,  for  we  have  depended 
upon  the  experiments  of  Joule  and  Thomson  and  on  the 
law  of  adiabatic  expansion;  however,  the  approximation 
is  more  close.  If  it  seems  sufficient  for  air,  it  is  certainly 
not  so  for  carbonic  acid.  Neither  is  the  formula  rigor- 
ously exact  for  air. 

Callendar  has  calculated  the  correction  to  make  to  the 
air-thermometer  readings  by  extrapolation  up  to  1000°, 
and  he  found  the  following  results: 


Readings  of 
Centigrade 
Thermometer. 

Volume  Constant. 

Pressure  Constant. 

# 

dt 

* 

It 

0° 

0.001173 

0 

0.001173 

0 

100 

0.000627 

0 

0.000457 

0 

200 

393 

0.04 

225 

0.084 

300 

267 

0.09 

127 

0.20 

500 

147 

0.23 

52 

0.47 

1000 

54 

0.62 

12 

1.19 

The  deviations  of  the  air-thermometer  at  high  tem- 
peratures are  thus  very  slight  if  concordance  is  estab- 
lished at  0°  and  100°  and  we  have  seen  that  in  the  case  of 
nitrogen  the  experiments  of  Chappuis  and  Harker  have 
shown  the  same  to  be  true  for  this  gas.  In  an  experi- 
mental investigation,  not  yet  completed,  on  the  dilata- 
tions of  nitrogen,  air,  oxygen,  carbon  monoxide  and 
carbonic  acid  throughout  the  ran'ge  0°— 1000°  Jacquerod 
and  Perrot  find,  using  a  quartz  bulb  at  constant  volume, 
that  the  coefficients  of  the  first  three  remain  excessively 
close  together  throughout  this  range  and  that  the  coeffi- 
cient for  carbonic  acid,  although  less  than  in  the  0°— 100° 


32 


HIGH  TEMPERATURES. 


interval,  remains  considerably  greater  than  for  the  other 
gases. 

Callendar,  in  a  recent  computation  based  upon  the 
work  of  Kelvin  and  Joule  and  the  experiments  of  Chappuis 
and  others,  arrives  at  the  following  values  for  the  scale 
corrections  for  the  best  thermometric  gases: 

SCALE  CORRECTIONS  FOR  GASES,  ASSUMING  00  =273°.10. 


Constant  Pressure,  76  cms. 

Constant  Volume  p\  =  100  cms. 

Temp. 

Cent. 

Helium. 

Hydro- 

Nitro- 

Air. 

Helium. 

Hydro- 

Nitro- 

Air. 

gen 

gen. 

gen. 

-    150 

4-0.073 

+  0.084 

+  0.945 

+  0.901 

-0.026 

+  0.013 

+  0.195 

+  0.186 

-    100 

+    .030 

+    .022 

+    .328 

+    .314 

-    .012 

+    .005 

+    .080 

+    .076 

-      50 

+    .009 

+    .006 

+    .090 

+    .086 

-    .004 

+    .002 

+    .024 

+    .023 

-      20 

+    .003 

+    .002 

+    .025 

+    .024 

-    .001 

+    .000 

+    .007 

+    .007 

+      20 

-.0016 

-.0009 

-.0141 

-.0134 

+  .0008 

-.0003 

-.0043 

+  .0041 

+     40 

-  .0022 

-.0013 

-.0195 

-.0186 

+  .0011 

-.0004 

-.0059 

+  .  0056 

+     50 

-.0022 

-.0013 

-  .0195 

-.0186 

+  .0011 

-.0004 

-  .  0059 

+  .0056 

+     60 

-.0021 

-.0012 

-.0180 

-.0172 

+  .0011 

-  .  0004 

-  .0054 

+  .0053 

+     80 

-.0013 

-.0008 

-.0113 

-.0108 

+  .0007 

-.0002 

-.0038 

+  .0034 

+    150 

+  .0054 

+  .0029 

+    .043 

+    .041 

'-.0031 

+  .0010 

+  .0143 

+  .0136 

•+   200 

+  .0128 

+  .0068 

+    .101 

+    .096 

-.0076 

+  .  0024 

+  .035 

+  .033 

+  300 

+  .0332 

+  .0165 

+    .243 

+    .232 

-.203 

+  .0059 

+  .088 

+  .084 

+   450 

+  .071 

+  .034 

+    .495 

+    .472 

-.047 

+  .013 

+  .189 

+  .180 

+  1000 

+  .243 

+  .104 

+  1.53 

+  1.46 

-.187 

+  .044 

+  .646 

+  .616 

The  above  table  indicates  that  for  the  gases  hydro- 
gen and  helium  no  attention  need  be  paid  to  the  thermo- 
dynamic  correction,  for  it  is  quite  negligible  for  the  whole 
temperature  range  for  these  two  gases.  All  the  gases 
are  also  seen  to  have  a  greater  correction  at  constant 
pressure  than  at  constant  volume.  Again  it  is  to  be  noted 
that  at  small  initial  pressures  these  corrections  will  be 
proportionally  reduced,  and  finally  that  it  is  only  in  the 
most  refined  work  that  this  correction  need  be  applied, 
as  in  the  establishment  of  a  fixed  point  in  pyrometry 
as  the  gold  fusing-point. 


NORMAL  SCALE  OF  TEMPERATURES. 


33 


D.  Berthelot  has  indicated  a  simple  method  for  calcu- 
lating  this   thermodynamic   correction   for  any  gas. 
For  a  constant  volume  thermometer: 

T-T  =tl\       a    10°~^ 
0      \      373273  +  J/' 

T0  being  the  absolute  temperature  of  melting  ice  (273°.  10), 
T  the  absolute  temperature  sought  corresponding  to  the 
centigrade  temperature  t  given  by  the  gas-thermometer 
in  question  at  an  initial  pressure.  For  other  pressures  p 

the  correction  to  t  must  be  multiplied  by  ^. 
For  the  constant-pressure  thermometer 

.  273646  +  * 


373273  +  * 

The  value  of  a  depends  upon  the  critical  constants  of  the 
gas  and  is 

=64      '7? 

where  R  is  the  gas  constant  (here  ) ,  Tc  and  pc  the 

*  27 o .  I/ 

critical  pressure  and  temperature  respectively. 


TABLE    OF   CRITICAL    CONSTANTS. 


PC 

<c 

a 

Carbonic  acid  

72  9  atm. 

+  31  3 

2  188 

Oxygen.  . 

50.0 

—  118 

0.422 

Air  

39  0 

—140 

.342 

Carbon  monoxide.  .  •  

35.9 

—  141 

.363 

Nitrogen 

33  6 

—  146 

343 

Hydrogen.  . 

13.0 

-240 

.016 

Helium  

? 

? 

(small) 

34  HIGH  TEMPERATURES. 

The  formulae  of  Berthelot  give  practically  identical  values 
for  the  thermodynamic  corrections  as  found  by  Callendar. 
Experimental  science  has  now  reached  such  a  develop- 
ment that  as  above  stated  these  corrections  cannot  always 
be  neglected.  It  is  to  be  noted  in  confirmation  of  this 
statement  that  the  sulphur  boiling-point  as  determined 
by  Callendar  and  Griffiths  in  terms  of  a  constant-pres- 
sure thermometer  was  0°.2  lower  than  found  by  Chappuis 
and  Harker  on  the  constant-volume  scale,  a  difference 
practically  identical  with  that  indicated  by  the  above 
table. 

The  experiments  of  Kelvin  and  Joule  may  also  be  used 
to  determine  the  absolute  temperature  of  the  point  of 
fusion  of  ice  on  the  thermodynamic  scale.  Below  are 
the  results  of  a  computation  by  Lehrfeldt: 

Gas-ther.  Thermodyn.  Ther. 

Hydrogen 273°. 08          272°. 8 

Air 272  .43  273  .27 

Nitrogen 273  . 13  273  .2 

(  274  .83  (Thomson) 

Carbonic  acid 268  .47       \  Of70 

(  273  .48  (Natanson) 

The  thermodynamic  temperature  of  melting  ice  should  be 
in  all  cases  the  same;  the  deviations  come  mainly  from 
the  uncertainties  in  the  measurements  of  the  heat  of 
expansion,  indicating  the  desirability  of  repeating  Joule 
and  Thomson's  work  with  modern  appliances. 

A  later  calculation  by  Rose-Innes  based  on  the  recent 
work  of  Chappuis  shows  that  there  is  still  an  outstanding 
difference  of  0°.08  in  the  absolute  temperature  of  melting 
ice  as  given  by  hydrogen  and  nitrogen  and  suggests  that 
this  might  be  accounted  for  by  occlusion  on  a  very  small 
scale.  Further  experimental  evidence  on  this  point  is 
needed  and  the  absolute  value  of  the  ice-point  is  still 


NORMAL  SCALE  OF   TEMPERATURES. 


35 


uncertain  by  over  0°.l.  The  following  table  gives  Cal- 
lendar's  resume  of  the  expansive  properties  of  the  ther- 
mometric  gases.  In  the  table  60  is  the  thermodynamic 
temperature  of  the  ice-point  as  determined  from  hydro- 
gen, and  T0  this  point  on  the  various  gas-scales. 

EXPANSION    AND    PRESSURE    COEFFICIENTS    FOR    00=273°.10. 


Constant  Pressure  76  cm. 

Constant  Volume  po  =  100  cm. 

Gas. 

60  -To 

To 

VT0 

0o  -TO 

To 

yn 

Helium.  .  .  . 

+  0.10 

273.00 

.0036628 

+  0.19 

272.91 

.0036640 

Hydrogen.  . 

-    .135 

273.235 

.00365985 

+    .067 

273.034 

.00366254 

Nitrogen.  .. 

+    .70 

272.40 

.0036708 

+    .99 

272.11 

.00367466 

Air  

+    .71 

272.39 

.0036709 

+    .96 

272.14 

.00367425 

CHAPTER  II. 


NORMAL  THERMOMETER. 

Sevres  Thermometer. — This  thermometer  is  a  constant- 
volume  thermometer  filled  with  pure,  dry  hydrogen,  under 
the  pressure  of  1  m.  of  mercury  at  the  temperature  of 
melting  ice.  It  consists  of  ,  two  essential  parts :  the 
reservoir,  enclosing  the  invariable  gaseous  mass,  and  the 
manometer,  serving  to  measure  the  pressure  of  this  gase- 
ous mass. 

The  reservoir  is  made  of  a  platinum-iridium  tube  whose 
volume  is  1.03899  liters  at  the  temperature  of  melting  ice. 
Its  length  is  1.10  m.;  and  its  outer  diameter  0.036  m.  It 


FIG.  1. 

is  attached  to  the  manometer  by  a  capillary  tube  of 
platinum  of  0.7  mm.  diameter.  This  is  as  small  as  is 
safe  to  make  this  tube  on  account  of  the  otherwise  too 
slow  establishment  of  pressure  equilibrium. 

36 


NORMAL  THERMOMETER.  37 

This  reservoir  is  supported  horizontally  in  a  double 
box  with  interior  water  circulation.  For  the  determina- 
tion of  the  100°  mark,  indispensable  for  standardization, 
the  reservoir  can  be  placed  in  the  same  way  in  a  hori- 
zontal heater  supplied  with  steam  and  composed  of  sev- 
eral concentric  coverings. 

Manometer.  —  The  manometric  apparatus  is  mounted 
upon  an  iron  support  of  2.10  m.  height,  which  is  made  of 
a  railway  rail  firmly  bolted  to  a  tripod  of  wrought  iron. 
The  lateral  parts  attached  to  this  rail,  planed  their  entire 
length,  carry  sliding  pieces  to  which  are  fastened  the 
manometer  tubes  and  a  barometer.  Fig.  2  represents,  in 
a  slightly  modified  form,  the  manometric  apparatus.  It 
is  composed  essentially  of  a  manometer  open  to  the  air 
whose  open  arm  serves  as  cistern  for  a  barometer.  The 
other  arm,  closed  half-way  up  by  a  piece  of  steel,  is  at- 
tached to  the  thermometric  reservoir  by  the  capillary 
tube  of  platinum.  The  two  manometer  tubes,  each  of 
25  mm.  interior  diameter,  have  their  lower  ends  fixed 
into  a  block  of  steel.  They  communicate  with  each  other 
by  holes  of  5  mm.  diameter  bored  in  the  block.  A  stop- 
cock permits  closing  this  connection.  A  second  three- 
way  cock  is  screwed  on  the  same  block.  One  of  its 
branches  can  serve  to  let  mercury  run  out;  the  other,  to 
which  is  attached  a  long  flexible  steel  tube,  puts  the 
manometer  in  communication  with  a  large  reservoir  of 
mercury  which  can  be  raised  or  lowered  the  length  of  the 
support,  either  rapidly  by  hand,  or  slow-motioned  by 
means  of  a  screw. 

The  barometer  which  sets  in  .the  open  branch  is  fixed  at 
its  upper  part  on  a  carriage  whose  vertical  displacement  is 
regulated  throughout  a  length  of  0.70  m.  by  a  strong 
screw.  The  latter  is  held  at  its  two  ends  by  two  nuts 
which  permit  it  to  turn  without  longitudinal  motion;  it 


38^ 


HIGH   TEMPERATURES. 


works  in  a  screw  attached  to  the  carriage,  and  carries  at  its 
lower  end  a  toothed  pinion  which  works  into  a  cog-wheel. 
It  suffices  to  turn  this  wheel  by  acting  upon  the  rod  which 


FIG.  2. 

serves  as  axis  in  order  to  raise  or  lower  the  carriage  with 
the  barometer  tube.  This  last  has  a  diameter  of  25  mm. 
in  its  upper  part.  The  chamber  is  furnished  with  two 
indices  of  black  glass  soldered  to  the  interior  of  the  tube 


NORMAL   THERMOMETER.  39 

at  0.08  m.  and  0.16  m.  from  the  end.  The  points  of  these 
indices,  convex  downwards,  coincide  sensibly  with  the  axis 
of  the  barometric  chamber.  The  part  of  the  barometer 
which  fits  into  the  open  manometer  arm  has  a  diameter 
greater  than  0.01  m.,  and  ends  below  in  a  narrower  tube 
curved  upwards. 

The  piece  of  steel  which  ends  the  closed  arm  is  adjusted 
to  this  tube  like  a  cock,  leaving  between  itself  a*nd  the 
tube  but  a  very  slight  space,  which  is  filled  with  sealing- 
wax.  It  rests  upon  the  upper  rim  of  this  tube,  to  which 
it  is  besides  pressed  by  leather  washers  tightly  screwed 
up.  At  its  lower  end  it  terminates  in  a  perfectly  smooth 
polished  plane,  which  is  adjusted  to  be  horizontal.  In 
the  middle  of  this  surface,  near  to  the  opening  of  the 
canal  which  prolongs  the  joining  tube,  there  is  fixed  a 
very  fine  platinum  point,  whose  extremity,  meant  to  be 
used  as  a  reference-mark,  is  at  a  distance  of  about  0.6  mm. 
from  the  plane  surface. 

Above  this  piece  is  a  tube  of  25  mm.  interior  diameter, 
open  above  and  connected  below  to  the  open  arm  of  the 
manometer. 

Since  the  measurement  of  a  column  of  mercury  is  more 
easily  made  and  with  greater  precision  when  the  menisci 
whose  difference  of  level  it  is  desired  to  find  are  situated 
along  the  same  vertical,  the  barometer  is  bent  so  as  to 
bring  into  the  same  vertical  line  the  axis  of  the  closed 
arm  of  the  manometer  and  that  of  the  barometer.  Under 
these  conditions,  the  communication  between  the  two 
manometer  arms  being  established,  the  total  pressure  of 
the  gas  enclosed  in  the  reservoir  of  the  thermometer  is 
given  by  the  difference  of  level  of  the  mercury  in  these 
superposed  tubes. 

The  measurement  of  the  pressures  is  made  by  means 
of  a  cathetometer  furnished  with  three  telescopes,  each 


40  HIGH  TEMPERATURES. 

of  which  is  provided  with  a  micrometer  and  level.  The 
micrometer  circle  is  divided  into  100  parts;  at  the  distance 
from  which  the  manometer  is  read,  each  division  of  the 
circle  corresponds  to  about  0.002  mm. 

The  method  adopted  for  the  measurement  of  pressures 
consists  in  determining  the  position  of  each  mercury 
meniscus  in  terms  of  a  fixed  scale,  hung  near  the  manom- 
eter tubes,  at  the  same  distance  as  these  latter  from  the 
telescopes  of  the  cathetometer. 

One  of  the  principal  difficulties  arising  in  the  measure- 
ment of  pressures  is  that  of  the  lighting  of  the  menisci. 
The  m'ethod  employed  by  Chappuis  consists  in  bringing 
up  to  the  surface  of  the  mercury  an  opaque  point  until 
its  image  reflected  by  the  mercury  appears  in  the  observ- 
ing telescope  at  a  very  small  distance  from  that  of  the 
point  itself.  These  two  images  being  almost  in  contact, 
it  is  easy  to  set  the  micrometer  cross-wire  midway  between 
them,  at  the  precise  point  where  would  be  the  image  of  the 
reflecting  surface.  In  order  to  have  a  very  sharp  image 
of  the  point,  it  is  well  to  illuminate  from  behind  by  means 
of  a  beam  of  light  passing  through  a  vertical  slit.  The 
point  and  its  image  then  stand  out  black  on  a  bright 
background.  The  use  of  styles  of  black  glass  is  preferable 
to  that  of  steel  points  on  account  of  their  unchangeable- 
ness  and  of  the  greater  sharpness  of  their  edges. 

The  method  with  styles  cannot  be  advantageously  em- 
ployed except  in  wide  tubes,  where  the  reflecting  surface 
of  the  mercury  which  aids  in  the  formation  of  the  image 
does  not  have  a  sensible  curvature. 

Waste  Space. — This  consists  of  the  space  occupied  by 
the  gas:  (1)  in  that  part  of  the  capillary  tube  which  does 
not  undergo  the  same  variations  of  temperature  as  the 
thermometric  reservoir;  (2)  in  the  piece  of  steel  forming 
the  plug  which  caps  the  closed  arm  of  the  manometer; 


NORMAL   THERMOMETER.  41 

(3)  in  the  manometer  tube  between  the  mercury  and  the 
horizontal  plane  in  which  ends  the  piece  of  steel.  The 
mercury  is  supposed  to  just  touch  the  style  serving  as 
reference-mark. 

The  capacity  of  the  tube  has  been  determined  by  mer- 
cury calibration;  it  was  found  equal  to  0.567  cc.  The 
length  of  the  capillary  tube  being  1  m.,  if  we  deduct 
from  this  capacity  that  of  3  cm.  of  the  tube  which  are 
exposed  to  the  same  temperatures  as  the  reservoir,  that 
is  0.015  cc.,  this  leaves  0.552  cc. 

The  capillary  tube  fits  for  a  length  of  27  mm.  into  the 
piece  of  steel  serving  as  plug.  The  total  thickness  of 
this  plug  is  28.3  mm. ;  thus  the  portion  of  the  canal  included 
between  the  end  of  the  capillary  tube  and  the  lower  face 
of  the  plug  is  1.3  mm.  in  length.  As  its  diameter  is  1.35 
mm.,  the  capacity  of  this  canal  is  0.0019  cc. 

The  space  included  between  a  cross-section  of  the 
manometer  tube  passing  through  the  style  and  the  plane 
surface  of  the  plug  is  0.3126  cc. 

To  have  the  total  volume  occupied  by  the  gas  it  is 
necessary  to  add  as  well  to  this  space  the  volume  of  the 
depressed  mercury  in  the  manometric  tube  caused  by  the 
curvature  of  the  meniscus.  The  radius  of  this  tube  being 
equal  to  12.235  mm.,  we  find  for  this  volume  0.205  cc. 

We  thus  have  as  the  total  of  the  waste  space  the  sum  of 
the  following  volumes: 

Cc. 

Capacity  of  capillary  tube. 0.5520 

Volume  of  canal  in  the  plug 19 

Capacity  of  the  manometer  tube  between  the  style 

and  the  plane 3126 

Volume  of  depressed  mercury 2050 

Total  waste  space 1 .0715 


42  HIGH  TEMPERATURES. 

When  the  mercury  does  not  just  touch  the  style,  we  shall 
have  to  add  to  this  value,  0.4772  cc.  per  millimeter  sepa- 
ration of  the  style  from  the  top  of  the  meniscus. 

The  expansion  of  the  metal  of  the  bulb  has  been  measured 
by  Fizeau's  method;  this  volume  has  at  different  tem- 
peratures the  following  values: 

Liters. 

20° 1.03846 

0 , 1.03899 

20 1.03926 

40  1.04007 

60  1.04061 

80 .«.  1.04117 

100  1.04173 

The  variation  of  the  capacity  of  the  bulb  due  to  changes 
of  pressure  has  also  been  studied;  per  millimeter  of  mer- 
cury it  is  0.02337  mm.  ;  or 

For  0  mm 0  mm. 3 

"  100           2.3 

"  200           4.7 

"  300           7.0 

"  400           9.3 

The  zero  is  verified  from  time  to  time  by  bringing  the 
bulb  to  the  temperature  of  melting  ice;  there  is  absolute 
constancy  even  after  -heating  to  100°.  The  deviation  is  at 
the  most  0.03  mm.  for  a  pressure  of  995  mm. 

Callendar's  Thermometer. — For  the  graduation  of  the 
platinum  resistance-thermometer  Callendar  has  studied  an 
arrangement  of  the  gas-thermometer  in  which  the  waste 
space  is  reduced  to  a  minimum  by  an  ingenious  device 
which  consists  in  interposing  in  the  capillary  tube  a 
column  of  sulphuric  acid  which  is  always  brought  to  the 


NORMAL   THERMOMETER. 


43 


same  position.  It  is  then  permissible  to  leave  vacant 
spaces  in  the  manometer  of  any  volume,  and  this  sim- 
plifies the  measurements. 

The  bulb  is  of  glass,  and  its  capacity  is  77.01  cc.  The 
capillary  tube  has  a  diameter  of  0.3  mm.  It  is  attached 
to  a  small  U  tube  of  2  mm.  diameter  which  contains  the 
sulphuric  acid.  The  total  value  of  the  waste  space  is  thus 
reduced  to  0.84  cc. 

The  sulphuric  acid  before  each  measurement  is  brought 
up  to  a  reference-mark.  The  density  of  this  liquid  being 
one-seventh  that  of  mercury,  the  errors  made  in  deter- 


Thermometre 


Manometre 


FIG.  3. 

mining  its  level  should  be  divided  by  seven  to  express 
them  in  heights  of  mercury.  The  use  of  this  column  of 
sulphuric  acid  has  the  inconvenience  to  oblige  the  experi- 
menter to  watch  constantly  the  apparatus  during  the  whole 
time  of  heating  and  cooling  in  order  to  maintain  the  pres- 


44 


man  TEMPERATURES. 


sure  equilibrium  in  the  two  parts  of  this  column;  other- 
wise the  liquid  would  be  driven  into  the  manometer  or 
absorbed  into  the  bulb. 

The  manometer  is  one  open  to  the  air  and  is  read  con- 
jointly with  the  height  of  the  barometer. 

The  coefficient  of  expansion  of  the  hard  glass  used  in  the 
construction  of  the  thermometer  was  measured  for  a  tube 
of  same  make  by  means  of  two  microscopes  carried  upon 
a  micrometer-screw.  A  cold  comparison-tube  could  be 
placed  under  the  microscopes  to  verify  the  invariability  of 
their  distance  apart. 

MEAN    COEFFICIENT   OF   EXPANSION. 

t  a 

17° 0.00000685 

102 706 

222 740 

330 769 

481 810 

After  heating  to  400°  there  were  permanent  changes 
amounting  to  from  0.02  to  0.05  per  100. 

If  the  zero  is  taken  at  intervals  of  time  of  varying 
length,  permanent  displacements  are  noted.  The  follow- 
ing table  gives  some  examples: 


Date. 

Oxygen- 
thermometer. 

Nitrogen- 
thermometer. 

Remarks. 

mm. 

mm. 

Jan.  21,  1886 

693.1 

695.4 

\  Filled  at  300°;  measure- 
)    ment  taken  4  days  later 

"      22,     " 

692.9 

695.1 

"     23,     " 

692.9 

694.9 

After  heating  to  100° 

"     25,     " 

692.0 

693.8 

"     25,     " 

692.0 

694.1 

u        (i         ti      a 

NORMAL  THERMOMETER.  45 

This  change  of  zero  has  been  attributed  to  a  partial 
absorption  of  the  air  by  the  glass.  Glass,  an  amorphous 
body  resembling  liquids  somewhat,  dissolves  gases,  espe- 
cially at  high  temperatures. 

For  temperatures  higher  than  300°  this  source  of  error 
becomes  very  serious,  especially  if  the  gas  is  hydrogen. 
This  gas  disappears  progressively  by  solution  in  the  glass 
or  by  oxidation  replacing  elements  of  the  glass.  It  is 
necessary  to  revert  to  nitrogen.  This  fact  was  observed 
by  Chappuis  and  Harker  in  the  course  of  a  study  of  the 
platinum  resistance-pyrometer  when  the  temperatures 
measured  reached  as  high  as  600°. 

One  of  the  more  recent  forms  of  this  thermometer  in 
which  there  is  complete  compensation  of  the  waste  space 
is  shown  in  Fig.  4,  where  A  is  the  thermometer  bulb  con- 
nected by  a  capillary  a  to  an  overflow  bulb,  or,  as  here 
shown,  to  a  burette  B.  The  compensating  capillary  b  is 
also  connected  to  a  bulb  C,  and  across  the  two  capillaries 
a  and  6  is  inserted  the  differential  manometer  D.  The 
bulbs  C  and  B  for  most  exact  work  should  be  enclosed 
in  a  bath  at  constant  temperature,  as  an  ice  bath.  The 
relative  sizes  of  the  bulbs  for  the  greatest  accuracy  will 
depend  upon  the  temperature  range  to  be  studied.  When 
equilibrium  and  compensation  are  established  at  any  tem- 
perature the  mass  of  the  gas  in  the  two  parts  of  the  appa- 
ratus will  be  the  same  if  the  pressures  are  adjusted  to  equal- 
ity as  shown  by  the  sensitive  manometer  D,  this  supposing 
that  C  and  B  are  at  exactly  the  same  temperature.  For 
a  change  in  temperature  the  volume  change  of  the  gas  in 
B,  i.e.,  forced  over  from  A,  may  be  made  by  reading  this 
volume  on  the  burette  or  better  by  weighing  the  dis- 
placed mercury.  The  upper  stop-cock  serves  to  exhaust 
and  fill  the  apparatus. 


46 


HIGH  TEMPERATURES 


ETC.  4. 


NORMAL  THERMOMETER.  47 

A  determination  of  temperature  is  made  as  follows:   for 
the   compensating  side   of  the   apparatus   we   have 

V0 = volume  of  gas  in  C ; 

m0=mass  "    " 

#0=  temperature  "    ".""  on  gas  scale; 
p0=pressure      '   "    "    "  " 
v  =  volume  of  capillaries; 
6  =  average  temperature  of  capillaries. 
Then 


where  k  is  a  constant. 

For  the  thermometer  proper  we  have,  using  a  similar 
notation, 


the  subscript  t  referring  to  A,  and  m  to  B. 

But  ml=m  and  pt=Po  as  conditions  of  compensation; 
therefore 

^t  ,  la    I, 

' 


But  C  and  B  are  at  the  same  temperatures,  00,  or  0m=0 
FinaUy 


Used  with  a  quartz  or  platinum  bulb  such  a  gas-ther- 
mometer may  become  an  instrument  of  the  greatest 
accuracy  for  the  experimental  extension  of  the  gas  scale 
at  constant  pressure. 

Thermometer  for  High  Temperatures. — Up  to  the 
present  time  there  has  not  yet  been  realized  for  the  meas- 


48  HIGH  TEMPERA  TURES. 

urement  of  high  temperatures  a  gas-thermometer  suffi- 
ciently precise  to  be  considered  a  normal  apparatus  unless 
it  be  that  of  Holborn  and  Day,  who  have  unquestionably 
carried  the  gas -scale  up  to  1150°C.  in  a  most  satisfactory 
manner.  We  shall  point  out,  in  studying  the  gas-pyrom- 
eters, the  conditions  that  such  an  apparatus  should  fulfil, 
and  the  reasons  for  these  conditions.  We  shajl  in  this 
place  give  only  a  brief  summary. 

The  gas  should  be  nitrogen  or  possibly  helium. 

The  bulb  should  be  of  some  platinum  metal,  as  80  Pt- 
20  Ir,  or  possibly  quartz  up  to  1200°  C. 

The  measurements  should  be  made  by  the  method  of 
the  thermo-volumenometer  or  by  any  other  method 
which  does  not  entail  an  invariability  of  the  gaseous  mass 
throughout  a  very  considerable  period  of  time. 

In  its  actual  condition  the  normal  Sevres  thermometer 
permits  of  measurements  up  to  100°. 

That  of  Callendar  has  been  employed  up  to  600°,  and 
could  without  doubt  with  a  porcelain  bulb  be  used  up  to 
1000°,  or  even  higher  with  quartz  or  platinum. 

Holborn  and  Day  have  obtained  most  consistent  re- 
sults up  to  1150°  with  a  constant- volume  nitrogen-ther- 
mometer in  a  80  Pt-20  Ir  bulb  of  200  cc.  capacity. 

It  would  be  possible  to  reach,  by  the  method  of  the 
volumenometer,  1300°.  To  go  higher  it  would  be  neces- 
sary to  manufacture  a  special  porcelain  less  fusible  than 
the  ordinary  hard  porcelain,  or  preferably  use  platinum 
or  one  of  its  alloys  in  an  oxidizing  atmosphere,  by  which 
means  it  might  be  possible  to  reach  1600°. 


CHAPTER  III. 
GAS-PYROMETER. 

THE  gas-thermometer,  as  we  have  seen  above,  need  not 
of  necessity  be  used  for  the  measurement  of  temperatures; 
it  suffices  to  make  use  of  it  for  the  standardization  of  the 
different  processes  employed  in  the  determination  of  tem- 
peratures, but  a  priori  there  are  not  on  the  other  hand 
any  absolute  reasons  for  discarding  it  in  cases  other  than 
these  standardizations.  Indeed  it  has  often  been  em- 
ployed. We  shall  examine  some  of  the  various  trials  that 
have  been  made  with  it,  and  discuss  the  results  obtained. 

Substance  of  the  Bulb. — The  most  important  point  to 
consider  is  the  choice  of  the  substance  which  constitutes 
the  bulb ;  it  is  necessary  to  know  its  expansion  to  account 
for  the  variation  of  its  volume  under  the  action  of  heat; 
one  must  be  sure  of  its  impermeability. 

Five  substances  have  been  used  up  to  the  present  time 
to  make  these  bulbs:  platinum,  iron,  porcelain,  glass,  and 
quartz. 

Platinum,  in  spite  of  its  high  price,  was  employed  by 
Pouillet  and  Becquerel;  it  has  the  advantage  over  iron 
in  not  being  oxidizable,  over  porcelain  in  not  being 
fragile.  Its  coefficient  of  expansion  increases  in  a  regular 
manner  with  temperature: 

Between  0°  and  100°.     Between  0°  and  1000°. 

Mean  linear  coefficient 0 . 000007  0 . 000009 

49 


50  HIGH  TEMPERATURES. 

In  the  course  of  a  noted  controversy  between  H.  Sainte- 
Claire-Deville  and  E.  Becquerel  the  former  of  those  savants 
discovered  that  platinum  was  very  permeable  to  hydro- 
gen, a  gas  whose  presence  is  frequent  in  flames  at  points 
where  the  combustion  is  not  complete.  Platinum  was 
accordingly  completely  abandoned,  perhaps  wrongly,  it 
is  possible,  in  very  many  cases,  to  be  sure  of  the  absence  of 
hydrogen,  and  the  very  precise  experiments  of  Randall 
have  shown  that  red-hot  platinum  was  quite  impermeable 
to  all  gases  other  than  hydrogen,  even  with  a  vacuum 
inside  the  apparatus. 

Chappuis  used  a  liter  platinum-iridium  bulb  in  his 
researches  on  the  normal  gas  scale ;  and  in  the  later  investi- 
gations of  Holborn  and  Day  at  the  Reichanstalt  in  their 
comparison  of  thermocouple  indications  with  the  nitrogen 
scale  up  to  1150°C.,  bulbs  of  this  material  replaced  por- 
celain to  great  advantage.  As  much  iridium  (15  to  20  per 
cent.)  was  contained  in  the  alloy  as  permitted  its  shaping, 
giving  an  extremely  rigid  bulb  and  if  the  walls  are  1.5  mm. 
thick,  one  which  undergoes  no  appreciable  deformation 
after  being  subjected  to  the  considerable  pressures  re- 
quired in  the  constant-volume  gas-thermometer  at  high 
temperatures.  This  alloy  is  also  impermeable  to  nitrogen, 
but  must  be  guarded  against  reducing  gases  and  silicates 
at  high  temperatures. 

Holborn  and  Day  also  determined  the  coefficients  of 
expansion  of  platinum,  as  well  as  other  metals,  alloys  and 
porcelain. 

For  platinum  and  platinum-iridium  they  found : 

Platinum  :  M09=886&+ 1.324*2  from  0°  to  1000°; 
80Pt-20Ir  :  X- 109= 81984-1-1. 41&2    "    0°  "  1000°. 

These  determinations  were  made  on  bars  nearly  50  cm. 
long  in  a  most  carefully  constructed  comparator  heated 


GAS-PYROMETER.  51 

electrically.  The  uniformity  of  the  expansion  of  platinum 
is  shown  by  the  fact  that  Beno'it's  determination  by 
Fizeau  's  method  in  the  interval  0°  —  80°  C.  gave 


So  that  in  this  case  extrapolation  of  over  900°  C.  leads  to 
no  serious  error. 

Iron  has  but  one  advantage,  its  cheapness;  it  is  as 
permeable  to  hydrogen  as  is  platinum;  it  is  not  merely 
oxidizable  in  the  air,  but  is  besides  attacked  by  carbonic 
acid  and  water-vapor.  Thus  the  only  gas  that  can  be 
used  with  iron  is  pure  nitrogen.  The  coefficient  of  expan- 
sion of  iron  is  greater  and  increases  more  rapidly  than 
that  of  platinum: 

Between  0°  and  100°.     Between  0°  and  1000°. 
Mean  linear  coefficient  .....  0  .  000012  0  .  000015 

Also  this  increase  is  not  regular;  there  is  produced  at 
850°,  at  the  instant  of  the  allotropic  transformation,  a 
sudden  change  of  length,  a  contraction  of  0.25  per  cent. 

It  is  very  difficult  to  obtain  pure  iron;  very  small  quan- 
tities of  carbon  modify  somewhat  the  value  of  the  coeffi- 
cient of  expansion.  Besides,  the  change  of  state  of  steel 
at  710°,  corresponding  to  recalescence,  is  accompanied  in 
the  heating  by  a  linear  contraction,  varying  with  the 
amount  of  carbon  present,  from  0.05  to  0.15  per  cent. 

Iron  cannot  therefore  be  seriously  considered  for  work 
of  any  precision. 

Porcelain  was  adopted  as  a  result  of  the  discussion 
between  H.  Sainte-Claire-Deville  and  Becquerel;  it  was 
considered  as  absolutely  impermeable,  but  without  decisive 
tests, 


52  HIGH   TEMPERATURES. 

Even  well-baked  porcelain  consists  of  a  paste  somewhat 
porous  and  permeable;  it  is  only  the  glazing  that  assures 
its  impermeability.  But  this  covering  may  sometimes  not 
be  whole;  as  it  softens  above  1000°,  it  is  susceptible  of 
cracking  if  left  for  a  considerable  time  with  an  excess  of 
pressure  on  the  interior  of  the  apparatus.  According  to 
Holborn  and  Wien,  the  glazing  is  broken  after  reaching 
1100°,  when  a  considerable  difference  of  pressure  is  estab- 
lished in  the  direction  of  the  lifting  up  of  this  glazing. 

Finally  like  all  verres,  porcelain  dissolves  gases,  and  in 
particular  water-vapor,  which  passes  through  it  quite 
readily.  A  pyrometer  left  a  long  time  in  the  flame  at 
about  1200°,  becomes  filled  with  water-vapor  which  can 
be  seen  to  condense  in  the  manometer  after  a  few  weeks. 

The  experiments  of  Crafts 'have  shown  that  the  rapidity 
of  the  passage  of  water-vapor  through  porcelain,  in  a 
pyrometer  of  from  60  to  70  cc.  capacity  at  the  tempera- 
ture of  1350°,  was  0.002  grm.  of  water-vapor  per  hour. 

It  is  thus  not  safe  to  employ  porcelain  at  temperatures 
higher  than  1000°,  at  least  not  in  the  thermometric  proc- 
esses which  .  suppose  the  invariability-  of  the  gaseous 
mass. 

The  expansion  of  porcelain  has  been  the  object  of  a 
great  number  of  measurements  which,  for  porcelains  of 
very  different  make,  give  values  near  to  one  another;  the 
mean  linear  coefficient  between  0°  and  1000°  varies  be- 
tween 0.0000045  and  0.000005  for  hard  porcelain— that  is 
to  say,  baked  for  a  long  time  at  a  temperature  in  the 
neighborhood  of  1400°. 

Here  are  the  results  of  experiments  made  by  Le  Chate- 
lier  and  by  Coupeaux;  the  experiments  were  made  with 
porcelain  rods  100  mm.  in  length,  and  the  numbers  express 
the  elongation  of  these  rods  in  millimeters: 


GAS-PYROMETER. 


53 


Porcelain 

Temperatures  . 

0° 

200° 

400° 

600° 

800° 

1000° 

Bayeux 

0.075 
.078 
.076 
.090 

0.166 
.170 
.16? 
.I8f 

0.266 
.270 
.268 
.290 

0.367 
.378 

.360 
.390 

0.466 
.470 
.465 
.490 

Sevres  dure  (cuite  a  1400°).  .  .  . 
Limoges  

.... 

Sevres  nouvelle  (cuite  a  1400°)  . 

These  numbers  should  be  multiplied  by  three  to  give  the 
cubical  expansion. 

Porcelain  has  still  another  inconvenience;  the  glazing 
is  usually  put  on  the  outside  only  of  vessels,  so  that  the 
porosity  of  the  paste  gives  an  uncertainty  due  to  the 
unequal  absorption  of  gases  at  increasing  temperatures. 

According  to  Barus,  it  is  impossible  to  fill  with  dry  ah* 
a  pyrometer,  not  glazed  inside,  at  ordinary  temperatures. 
The  water  is  not  driven  out  by  pumping  out  several  times 
and  letting  in  dry  air.  An  apparatus  filled  in  this  way 
will  indicate  between  melting  ice  and  boiling  water  from 
150°  to  200°.  Nor  is  filling  the  apparatus  at  100°  satis- 
factory: it  will  indicate  115°  for  this  same  interval  of 
100°.  Barus  thinks  that  at  400°,  by  repeating  the  opera- 
tion several  times,  one  can  consider  the  apparatus  as 
filled  with  dry  air. 

The  use  of  porcelain  bulbs  in  several  recent  pyrometric 
researches  of  great  importance  has  been  the  cause  of 
outstanding  differences  in  the  determination  of  fixed 
points  in  pyrometry  as  the  sulphur  boiling-point,  that  are 
due  mainly  to  the  uncertainties  in  the  expansion  coeffi- 
cient of  the  particular  samples  of  porcelain  used. 

The  work  of  Chappuis,  Tutton,  Bedford,  and  of  Holborn, 
Day,  and  Griineisen  has  shown  the  expansion  of  porcelain 
to  be  anomalous  and  that  therefore  extrapolation  for 


54  HIGH   TEMPERATURES. 

the  coefficient  cannot  safely  be  made  even  over  a  hun- 
dred degrees  for  the  most  exact  work.  There  is  always 
a  deformation  of  the  bulbs  of  uncertain  and  irregular 
amounts  in  a  constant-volume  thermometer  sufficient  to 
render  results  doubtful  at  temperatures  as  low  as  500°  C., 
and  Holborn  and  Day  were  unable  with  porcelain  bulbs 
to  get  any  considerable  precision  at  1000°  C.,  and  finally 
discarded  them  entirely. 

They  found  for  the  expansion  of  Berlin  porcelain 

X  •  109  =  {  2954*  +  1  .  125£2  }  from  0°  to  1000°, 

but  this  value  is  too  high  for  temperatures  below  250° 
as  indicated  by  Chappuis,  and  Holborn  and  Griineisen 
have  shown  that  at  about  700°  C.  a  considerable  change 
in  the  coefficient  takes  place,  the  expansion  becoming 
more  rapid  at  higher  temperatures. 

It  would  probably  not  be  worth  while  to  make  further 
pyrometric  studies  with  porcelain  bulbs,  when  possible 
to  avoid  their  use. 

Glass  cannot  be  used  above  550°  C.,  but  in  this  range  it 
may  replace  porcelain  to  advantage  if  Jena  Borosilicate 
59in  is  used,  as  the  deformation  after  heating  is  some- 
what less  and  more  uniform.  The  coefficient  of  expansion 
of  this  glass  as  measured  in  the  form  of  capillary  tubes 
by  Holborn  and  Griineisen  is 


Quartz,  in  the  amorphous  or  fused  form,  can  now  be 
made  in  vessels  of  several  hundred  cubic  centimeters 
capacity,  thanks  to  many  attempts  culminating  success- 
fully in  the  efforts  of  Heraeus,  and  Siebert  and  Ktihn. 
The  chemical  and  physical  properties  in  view  of  its  py- 
rometric use  have  been  studied  by  many  investigators, 


GAS-PYROMETER.  55 

Shenstone  being  a  pioneer  in  advocating  its  use  in  ther- 
mometer bulbs.  Vitrified  quartz  vessels  seem  to  resist 
deformation  at  very  high  temperatures,  the  upper  limit 
when  the  interior  is  a  vacuum  being  not  far  from  1300°  C. ; 
the  substance  is  appreciably  plastic  at  1500°,  but  a  quartz 
vessel  will  not  collapse  until  2000°  is  reached,  according 
to  Heraeus. 

Fused  quartz  is  attacked  by  alkalies,  and  the  slightest 
trace  of  such,  as  from  handling,  may  do  damage  when  the 
heating  is  carried  very  high.  Weak  acids  and  neutral 
salts  are  without  effect  as  shown  by  Mylius,  but  at  high 
temperatures  all  oxides  attack  it.  Heated  with  a  porce- 
lain tube  to  very  high  temperatures  the  quartz  tends  to 
lose  its  transparency,  and  Moissau  has  shown  that  it  is 
slightly  soluble  in  a  lead  bath  above  1100°C.,  and  very 
much  more  so  in  zinc.  Villard  showed  that  it  is  perme- 
able to  hydrogen  but  less  so  than  platinum,  nor  does  it 
seem  to  occlude  other  gases;  it  is  less  brittle  than  por- 
celain. 

Its  great  advantage  in  gas  thermometry  is  its  lack  of 
deformation  and  its  extremely  small  coefficient  of  expan- 
sion, about  -fa  that  of  platinum,  or,  more  exactly,  as  deter- 
mined by  Holborn  and  Henning  with  a  comparator: 

;.  109=540£  from  0°  to  1000°. 
Scheel,  using  a  Fizeau  apparatus,  finds 

>l  - 109 = 322Z  + 1  A7t2  between  0°  and  100°, 

where  the  curvature  is  of  the  same  order  as  for  metals. 
In  work  at  1000°  C.  the  expansion  correction  is  reduced 
from  over  20°  with  porcelain  or  platinum  to  about  1°, 
and  its  uncertainties  become  therefore  negligible,  permit- 
ting a  great  increase  in  accuracy.  Several  investigations 


56  HIGH   TEMPERATURES. 

are  now  under  way  using  quartz  bulbs,  and  a  final  judg- 
ment as  to  its  availability  will  have  to  await  the  com- 
pletion of  this  work. 

Corrections  and  Causes  of  Error.  —  1.  Thermometer  at 
Constant  Volume.  —  We  must  now  render  more  precise  the 
formula  of  the  air-thermometer,  by  taking  account  of  the 
variations  of  volume  of  the  bulb,  of  the  surrounding  air- 
temperature  which  changes  the  density  of  the  mercury, 
and  finally  of  the  volume  of  the  waste  space. 

We  have  three  series  of  observations  to  make  in  order 
to  determine  a  given  temperature: 


(1) 


100100 

PV=nRT  ........    (3) 

Putting 


the  first  two  series  serve  to  determine  —  . 

a 

It   is   preferable,   except   in   researches   of  very  great 
precision,  to  take  —  from  previously  obtained  results,  and 

not  to  make  the  observations  at  100°,  unless  one  does  so 
to  check  his  experimental  skill. 

Dividing  the  third  equation  by  the  first,  we  have  the 
relation 

PV_      HA,V       nRT  =  nT 
P070     HQAV,      n0RTQ     n0T0> 

where  H  and  H0  are  the  heights  of  mercury,  A  and  J0  the 
densities  of  this  metal. 

For  a  first  approximation  let  us  neglect  the  differences 


GAS-PYROMETER.  57 

between  V  and  V0,  n  and  n0,  J  and  J0.     We  shall  have 
then  an  approximate  value  T'  for  the  temperature  sought : 

r=l'f/  •  •  •  • •••  •  •  (5) 

for 


Let  us  find  now  the  correction  dT  to  T7'  to  obtain  the 
exact  temperature.  In  order  to  find  this,  take  the  loga- 
rithmic differential  of  (4)  : 

dT    dJ    dV    dn 


Then  determine  the  values  of  the  different  terms;  let  tl 
and  t2  be  the  absolute  temperatures  of  the  surroundings 
when  the  bulb  is  at  the  temperatures  T'  and  T0. 


=  -o.oooi8(«2  - 


*• 


^(porcelain)  =  0.0000135., 

dV 
^-=0.0000135(77/-!T0), 

^0 

by  neglecting  the  variations  of  volume  of  the  bulb  due  to 
changes  of  pressure, 


58  HIGH   TEMPERATURES. 

\ 

3  dn=x2-xl 

nQ        n0 

in  calling  x2  and  xx  the  number  of  molecules  contained  in 
the  waste  space  £  at  the  temperatures  t2  and  tv  We  have 
in  fact,  N  being  the  total  mass  contained  in  the  apparatus, 

n=N-x2, 


To  determine  x1  and  x2: 


tr  Q£  =x^Kt^j 
Pe=x2Rt2, 


n0     VQ\t2 
In  noting  that 

we  have 

Put 

*=^ 


After  substitution  we  have 


'-TQ     6 


nQ        VQ\     t          t        t 


.       GAS-PYROMETER.  50 

These  successive  transformations  are  for  the  purpose  of 
making  evident  from  the  formula: 

1.  The  ratio  between  the  waste  space  and  the  total 

volume:  ==-; 
"o 

2.  The  temperature  measured:  T'-T0; 

3.  The  variation  of  the  surrounding  temperature  0; 
which  are  the  three  essential  factors  on  which  depends 
the  correction  in  question. 

Formula  (6)  then  becomes: 

'  =  ~  0.00018(<2  -  y  +  0.0000135(  T  -  T0) 


_      /T7' T*       ft    *T* T* 

C-V  -i        7      «    / 


Let  us  take  a  numerical  example  in  order  to  show  the 
importance  of  these  correction  terms  in  the  three  follow- 
ing cases: 

T'-T^  500°, 


T-  T0  =  1500°. 
In  taking 


*=27°+273°=300°, 
2^  =  10°, 
we  have 

^500=-   1°.4+  5°.15  +  13°.1=  16°.85, 
^1000=-  2°.3  +  17°.0   +38°.2=  52°.9, 


d7Tl500=-30°.7  +  35°.7  +90°.0  =  122°.5. 

These  figures  show  the  very  great  importance  of  the  waste 
space,  whose  exact  volume  it  is  impossible  to  kno\       T!  is 


60  HIGH  TEMPERATURES. 

method  of  computation  of  the  corrections  by  logarithmic 
differentials  is  only  approximate,  and  is  not  sufficient  for 
real  measurements,  but  it  renders  more  clear  the  general 
discussion  of  the  causes  of  error. 

Let  us  see  what  uncertainty  in  the  temperature  may 
result  from  the  uncertainty  which  there  may  be  in  the 
volume  of  the  waste  space.  In  reality  there  is  a  continu- 
ous passage  from  the  high  temperature  of  the  pyrometer 
to  the  surrounding  temperature  on  a  length  which  may 
vary  from  10  to  30  centimeters,  according  to  the  thickness 
of  the  walls  of  the  furnace.  The  volumes  of  the  bulb  and 
of  the  waste  space  which  should  be  taken  in  order  that 
the  above  formulas  be  exact  should  be  such  that  the  real 
pressure  is  equal  to  the  pressure  that  would  exist  in  sup- 
posing that  a  complete  and  sudden  change  of  tempera- 
ture took  place  at  a  definite  fictitious  point,  separating 
the  heated  part  from  the  cold  part  of  the  apparatus. 
The  probable  position  of  this  point  is  estimated,  and,  if 
the  estimation  is  poorly  made,  two  errors  are  committed, 
one  on  the  real  volume  heated  and  the  other  on  the  waste 
space,  errors  equal  and  of  opposite  sign  so  far  as  the 
volume  is  concerned. 

To  calculate  this  error,  as  in  the  case  of  the  corrections, 
we  may  employ  the  method  of  logarithmic  differentials. 

Applying  the  same  formula  as  before,  we  find  for  the 

dT 
relative  error  ~=~ : 

dT=     dV/T'-T0    6 
T  ~    ~  V0\     t          t 

and  neglecting  the  second  term  of  the  parenthesis,  which 
is  relatively  very  small, 

dT        dV/T'-T0\ 


GAS-PYROMETER.  61 

Letting  the  section  of  the  capillary  tube  be  equal  to 
I  sq.  mm.,  the  volume  of  the  bulb  100  cc.,  and  assumig 
an  uncertainty  of  100  mm.  in  the  position  of  the  tran- 
sition-point, a  value  often  not  exaggerated,  we  find  the 
following  errors  in  the  temperatures: 


We  thus  see  that  at  1000°  the  error  resulting  from  the 
uncertainty  in  the  origin  of  the  waste  space  may  reach 
several  degrees  for  a  bulb  of  100  cc. 

A  second  cause  of  error  results  from  the  changes  of 
mass  following  the  ingoings  and  outgoings  of  gas.  As 
before,  we  have 

dT==_dn 
T  ~      n0' 

Consider  the  experiments  of  Crafts.  There  enters  per 
hour  at  1350°  in  a  bulb  of  porcelain  of  100  c.c.,  0.002  grm. 
of  water-  vapor,  or  0.225  milligramme-molecules;  the 
initial  volume  enclosed  at  the  start  is  4.5  milligramme- 
molecules  : 

f  .235=0.05, 

which  leads  to  an  error  of 

dri350o=  70°  (about) 

for  an  experiment  lasting  one  hour. 

This  computation  demonstrates  clearly  the  enormous 
errors  which  may  result  from  the  penetration  of  an  outside 


62  HIGH  TEMPERATURES. 

gas  during  the  time  of  one  hour,  a  length  of  time  much 
less  than  that  of  an  ordinary  experiment.  It  is  true  that 
this  error  decreases  rapidly  with  rise  of  temperature,  and 
it  is  very  probably  zero  at  1000°,  if  there  is  no  break  in  the 
glazing. 

2.  Constant-pressure  Thermometer.  —  We  still  employ  the 
same  formula  (4)  : 

nRT 


which  gives  for  a  first  approximation 


n 


Calling  ^  and  t2  the  surrounding  absolute  temperatures 
corresponding  to  T0  and  7\,  u^  and  u2  the  corresponding 
volumes  of  the  waste  space  and  of  the  reservoir,  we  have, 
for  the  determination  of  n  and  n0,  the  relations: 


ft/Q  J.T  «/J  ,  .  , 

h'h 

n=N-x2=n0-(x2-x1), 
HAu2 


As  before,  there   is   a   correction   to   be  applied  to   the 
approximate  temperature  Tf  thus  obtained: 

d£    dH    dJ    dV 
T'~  H+  J0+  V0' 

an  expression  the  values  of  whose  terms  are  known. 


GAS-PYROMETER.  63 

Let  us  see  now  the  causes  of  error  and  discuss  their  im- 
portance. 

The  error  resulting  from  the  uncertainty  in  the  bound- 
ary of  the  hot  and  cold  volumes  is 

<W^dr^_dn^dn/  «_T\  =      dn^/T-T0\ 
T'     n0      n      n0\       TJ    .      n0  \     T0    I  * 

As  before  let, 

dn=    1 

n0~1000' 
Then  we  find 


Thus  the  errors  due  to  this  cause  are  still  greater  than  by 
the  method  of  constant  volume. 

In  order  to  make  exactly  the  correction  for  the  waste 
space,  the  method  of  Regnault's  compensator  maybe  em- 
ployed, as  in  the  work  of  Sainte-Claire-Deville  and  Troost; 
this  allows  of  placing  the  measuring  apparatus  at  a  con- 
siderable distance  from  the  fire,  which  makes  the  experi- 
ments much  easier. 

Let  us  now  examine  the  error  resulting  from  the  en- 
trance of  exterior  gases: 


For  the  experiment  of  Crafts,  the  error  would  be  413° 
instead  of  70°,  the  bulb  being  filled  at  the  start  at  atmos- 
pheric pressure. 

It  is  thus  evident  that,  from  all  points  of  view,  the 
method  of  constant  volume  is  more  precise  than  that  of 


64  HIGH  TEMPERATURES. 

constant  pressure;  the  lack  of  impermeability  of  the  cover- 
ings is  the  only  hindrance  preventing  the  use  of  the  former 
in  practice. 

3.  Volumenometric  Thermometer.  —  The  only  rational 
method  for  the  measurement  of  high  temperatures  is,  as  we 
have  already  said,  that  of  the  volumenometer  of  Becquerel, 
which  does  not  require  the  invariability  of  the  gaseous 
mass  throughout  the  duration  of  the  experiment.  It  con- 
sists in  measuring  the  changes  of  pressure  resulting  from 
a  given  variation  of  the  gaseous  mass  contained  in  the 
bulb.  Becquerel  employed  very  slight  changes  of  mass; 
the  changes  of  pressure  are  then  equally  slight,  which 
diminishes  the  precision  of  the  measurements. 

There  is  no  theoretical  inconvenience  in  reaching  an 
absolute  vacuum,  or,  what  is  practically  more  simple,  using 
the  exhaustion  given  by  a  water-pump,  as  was  done  by 
Mallard  and  Le  Chatelier;  this  considerably  increases  the 
precision.  If  the  exhaustion  is  complete,  we  have  the 
relation 


= 

RT'          RT 


UQ  being  the  volume  of  the  reservoir  corresponding  to  the 
surrounding  temperature  T0.  If  the  two  volumes  are  filled 
under  atmospheric  pressure,  P=P0,  and  then 

TL  * 

T0   v 

There  are  two  corrections  to  make:  the  first  relative  to 
the  expansion  of  the  envelope,  the  second  to  the  difference 
between  P  and  P0  when  the  exhaustion  is  produced  by  a 
water-pump  : 

dT^dP    dV 

T>  ~  P  +  y  ' 


GAS-PYROME  TER.  65 

In  general  dP  is  in  the  neighborhood  of  15  mm.  of 
mercury,  which  gives 


Also, 

dV 
^-=0.0000135(7T/-770), 


Calculating  this  correction  for  different  temperatures,  we 
have 


^1000=-  8.5, 
dT15W=-  0  .35. 

Let  us  compute  now  the  error  which  comes  from  the 
uncertainty  in  the  position  of  the  line  of  separation  of  the 
warm  part  and  the  cold  part  of  the  apparatus;  it  is, 
besides,  the  only  remaining  one: 

dT__dV 
T'~  V 

As  before,  assuming  the  higher  limit  to  be  y<sW> 

dT       1 
r'lOOO' 

which  leads  to 

,777     _n°  77 

a±  500    ~U    •'  'l 

dTim  =  l  .27, 
dr=2  .77. 


66  HIGH   TEMPERATURES. 

From  every  point  of  view,  this  method  is  thus  preferable 
to  the  others. 

This  whole  discussion  of  the  sources  of  error  in  the 
measurement  of  temperatures  aims  merely  to  obtain  a  deter- 
mination of  the  temperature  of  the  pyrometer  employed. 
But  this  temperature  is  in  itself  not  the  real  object  of  the 
measurements;  it  is  but  an  intermediary  to  arrive  at  a 
knowledge  of  the  temperature  of  certain  other  bodies 
supposed  to  be  in  thermal  equilibrium  with  the  pyrom- 
eter. Now  this  equilibrium  is  extremely  difficult  to  realize, 
and  it  is  more  often  the  case  that  there  is  no  way  of  being 
sure  of  the  exactitude  with  which  it  has  been  obtained. 
Here  is  then  a  new  source  of  error  very  important  in  the 
measurement  of  temperatures,  especially  of  high  tem- 
peratures, at  which  radiation  becomes  an  important  con- 
sideration. Within  an  enclosure  whose  temperature  is 
not  uniform,  which  is  true  for  the  majority  of  furnaces, 
there  may  exist  enormous  differences  of  temperatures 
between  neighboring  parts.  One  cannot  too  strongly 
insist  upon  the  presence  of  this  source  of  error,  with 
whose  existence  too  many  investigators  have  not  suffi- 
ciently occupied  themselves. 

Experimental  Results. — We  shall  study  now  the  experi- 
ments made  by  various  savants,  and  we  shall  see  in  what 
degree  the  conditions  of  precision  indicated  in  the  course 
of  this  account  have  been  realized. 

Experiments  of  Pouillet. — Pouillet  was  the  first  to  make 
use  of  the  air-thermometer  for  the  measurement  of  high 
temperatures;  he  obtained  very  good  values  for  the 
epoch  at  which  he  worked. 

His  pyrometer  was  made  of  a  platinum  bulb,  of  ovoid 
form,  of  60  cc.  capacity,  to  which  was  gold-soldered  a 
platinum  capillary  tube  of  25  cm.  in  length;  continu- 
ous with  this  tube  was  another  of  silver  of  the  same  length 


GAS-PYROMETER. 


67 


fastened  to  the  manometer.  The  joining  of  the  platinum 
and  silver  tubes  was  made  by  means  of  a  metal  collar 
(Fig.  5).  The  waste  space  had  thus  a  volume  of  2  cc. 


FIG.  5. 


The  manometer  was  made  up  of  three  glass  tubes  em- 
bedded at  their  lower  ends  in  a  metallic  piece;  the  first 
tube  serving  as  a  measurer  was  gradu- 
ated in  cubic  centimeters,  the  second 
constituted  the  manometer  properly 
speaking,  and  the  third  served  to  fill 
the  apparatus. 

A  cock  conveniently  placed  per- 
mitted variation  of  the  quantity  of 
mercury  contained  in  the  apparatus 
(Fig.  6).  The  principle  of  this  appa- 
ratus is  the  same  as  that  of  the  more 
recent  Regnault  manometer;  this  lat- 
ter differs  from  the  manometer  of 
Pouillet  only  in  the  suppression  of  the 
third  tube,  which  is  replaced  by  a 
bottle  joined  to  the  emptying-cock  by 
a  rubber  tube. 

Errors:    1.  According  to  Pouillet,  it 
was  impossible  to  carry  the  measure- 
ments up  to  1200°;  there  was  complete 
disaccordance  with  the  readings  of  the  mercury-thermom- 
eter.    He  attributed  this  non-agreement  to  the  condensa- 


68 


HIGH   TEMPERATURES. 


tion  of  air  on  the  platinum.  Becquerel  showed  later  that 
this  was  due  to  the  presence  of  water-vapor  in  the  insuffi- 
ciently dried  air. 

2.  Not  being  able  to  use  the  100°  mark  for  the  determi- 
nation of  the  coefficient  of  expansion  of  air,  Pouillet  took 
the  number  0.00375,  given  by  Gay-Lussac,  instead  of  the 
correct  number,  0.00367.  This  is  the  principal  source  of 
error  in  his  measurements.  The  following  table  permits  a 
comparison  of  his  results  for  the  specific  heats  of  platinum 
with  those  obtained  by  Violle: 


100° 

300° 

• 

500° 

700° 

1000° 

1200° 

Pouillet,  a  =0.00375.  . 
a=  0.00367... 
Violle  

0.0335 
32 
323 

0.0343 
336 
535 

0.0352 
345 
347 

0.0360 
353 
359 

0.0373 
366 
377 

0.0380 
373 
389 

Fusing-points. — Pouillet 's 
points  are  far  less  good: 


determinations     of    fusing- 


Gold 1180°  (too  high  by  115°) 

Silver 1000    (  "      "     "     40°) 

Antimony 432    (too  low  by  200°) 

Zinc 423    (good) 

The  possible  sources  of  error  are  the  following: 

1.  Introduction  of  hydrogen  into  the  platinum  bulb, 
which  should  raise  too  high  the  temperature-measurement 
and  diminish  the  specific  heat  of  platinum;    the  fusing- 
points  of  gold  and  silver  are  too  high. 

2.  Equilibrium  of  doubtful  temperature  with  the  fur- 
nace as  arranged.     A  glass  tube,  heated  from  below  by 
coal,  would  necessarily  be  more  strongly  heated  near  the 
base;  it  would  then  have  been  necessary,  in  order  to  have 
accurate   measurements   by   this    arrangement,    certainly 


GAS-PYROMETER. 


69 


very  irregular  as  to  temperature,  that  the  substance  and 
the  thermometer  be  in  the  same  conditions  with  respect 
to  radiation  (Fig.  7). 

For  antimony  the  error  is  certainly  due  to  some  particular 
cause;  or  perhaps  the  very  impure 
metal  was  mixed  with  lead,  or 
there  may  have  been  a  mistake  in 
computation.  Nevertheless  the 
number  432  was  the  only  one  used 
up  to  the  recent  memoir  of  Gautier 
on  the  fusibility  of  alloys. 

Experiments  of  Ed.  Becquerd. 
— This  savant  took  up  and  con- 
tinued the  work  of  Pouillet  with 
the  same  apparatus.  But  at  the 
close  of  a  discussion  with  H. 
Sainte-Claire-Deville  on  the  ques- 
tion of  the  permeability  of  plati- 
num, he  made  use  successively  of  pyrometers  of  iron  and 
of  porcelain.  The  results  obtained  with  platinum  seem, 
however,  to  be  far  the  best. 

Pyr.  of  Pt.  Pyr.  of  Porcelain. 

Boiling-point  of  zinc 930°  (good)  890° 

Fusing-point  of  silver 960        "  916 

Fusing-point  of  gold 1092  1037 

The  figures  for  gold  differ  among  themselves  by  about 
25°,  more  or  less. 

It  is  difficult  to  explain  these  differences,  which  are 
probably  due  to  inequality  of  temperature  between  the 
pyrometer  and  the  metal  under  investigation,  resulting 
perhaps  from  a  difference  in  their  emissive  powers. 

Experiments  of  H.  Sainte-Claire-Deville  and  Troost. — 
They,  after  their  discussion  with  Becquerel,  made  numer- 


FIQ.  7. 


70 


HIGH  TEMPERATURES. 


ous  experiments  with  the  porcelain  air-thermometer;  they 
obtained  very  discordant  results,  which  they  did  not  publish 
at  the  time. 

They  placed  the  most  confidence  in  the  determinations 
made  by  the  aid  of  the  vapor  of  iodine  (we  shall  speak  of 
this  later) ;  but  when  the  inaccuracy  of  this  method  was 
pointed  out,  they  made  known  the  results  that  they  had 
obtained  for  the  boiling-point  of  zinc. 

They  employed  a  crucible  of  plumbago  having  a  capacity 
of  15  grms.  of  zinc;  the  metal  was  added  anew  as  fast  as  it 
evaporated. 

The  crucible  was  placed  in  a  furnace  filled  with  coal. 
Around  the  pyrometer  was  arranged  a  covering  of  fire-clay  ; 
but  this  arrangement  was  quite  insufficient  to  eliminate 
errors  due  to  radiation.  The  same  measurements  were 
repeated  with  different  gases. 

Figures  obtained : 


Gas. 

First  Series. 

Second  Series. 

Third  Series. 

Air                             From 

945°  to  955° 

940°  to  948° 

928°  to  932° 

Hydrogen                     " 

925  to  924 

916  to  924 

C&rboiiic  8/cid  

1067 

1079 

The  deviations  seem  to  be  a  function  of  the  nature  of 
the  gas,  which  is  inexplicable;  it  would  be  necessary  to 
admit  of  an  enormous  dissociation  of  the  carbonic  acid  in 
order  to  explain  the  temperatures  found  with  this  gas. 

Later  this  method  was  modified.  The  gas  enclosed  in 
the  pyrometer  was  removed  by  means  of  the  mercury-pump, 
either  warm  or  after  cooling.  But  this  method  did  not 
possess  any  real  advantages;  the  entrance  of  the  gas  and 
vapors  during  the  reheating  is  not  avoided ;  besides,  during 
the  cooling,  there  is  danger  of  the  entrance  of  air  by  leak- 


GAS-PYROMETER.  71 

ing  of  the  cock  placed  at  the  outlet  of  the  pyrometer. 
Troost  found  in  this  way  665°  for  the  boiling-point  of 
selenium;  this  figure  is  too  high.  As  in  the  case  of  the 
determination  of  the  boiling-point  of  zinc,  the  arrangement 
for  heating  did  not  protect  sufficiently  against  the  radiation 
from  the  outer  surfaces. 

Violle's  Experiments. — Guided  by  H.  Sainte-Claire- 
Deville,  whom  his  successive  failures  had  instructed  in  the 
difficulties  of  the  problem,  Violle  has  made  a  series  of 
measurements  which  are  among  the  best  up  to  the  present 
time.  He  made  use  of  a  porcelain  thermometer,  and  he 
worked  simultaneously  at  constant  pressure  and  constant 
volume.  The  agreement  of  the  two  numbers  shows  if  the 
mass  has  remained  constant;  this  is  the  equivalent  of  the 
method  of  Becquerel. 

The  most  serious  objection  that  can  be  made  to  these 
observations  is  as  to  the  uncertainty  of  the  equality  of  tem- 
peratures of  the  pyrometer  and  of  the  substance  studied 
placed  beside  the  former;  from  this  point  of  view,  however, 
these  experiments,  made  in  the  Perrot  furnace,  were  much 
more  satisfactory  than  those  made  in  coal-furnaces  pre- 
viously employed. 

1.  A  first  series  of  determinations  was  of  the  specific 
heat  of  platinum.  A  platinum  mass  of  423  grm.  was  put 
into  a  Perrot  muffle  alongside  the  pyrometer,  and  when  the 
mass  was  in  a  state  of  temperature-equilibrium  it  was 
immersed,  either  directly  in  water  or  in  a  platinum 
eprouvette  placed,  opening  upward,  in  the  midst  of  the 
calorimeter-water.  In  the  first  case  the  experiment  was 
made  in  a  few  seconds;  in  the  second  it  lasted  fifteen 
minutes,  and  the  correction  was  as  high  as  0°.3  per  10°; 
the  results,  however,  were  concordant.  At  787°  two  experi- 
ments gave  0.0364  and  0.0366;  mean,  0.0365. 

At  1000°  twelve  experiments  were  made  employing  the 


72  HIGH  TEMPERATURES. 

method   of   immersion;    the   numbers   found   vary   from 
0.0375  to  0.0379;  mean,  0.0377. 

Near  1200°  the  measurements  were  made  at  constant 
pressure  and  at  constant  volume. 


Temperature 

Temperature 

Specific  Heat 

at  Constant 

at  Constant 

Mean. 

of 

Volume. 

Pressure. 

Platinum. 

1171° 

1165° 

1168° 

0.0388 

1169 

1166 

1168 

.0388 

1195 

1192 

1193 

.0389 

The  mean  specific  heat    may  be  represented  by  the 
formula 

C0<  =0.0317+0.000006-«. 

The  true  specific  heat  is  equal  to 


=  0.0317  +  0.000012-*. 
at 


Violle  used  these  determinations  to  fix,  by  extrapolation, 
the  fusing-point  of  platinum,  which  he  found  equal  to 
1779°.  He  measured  for  that  the  quantity  of  heat  given 
out  by  1  grm.  of  solid  platinum  from  its  fusing-point 
to  0°.  For  this  purpose  a  certain  quantity  of  platinum  is 
melted,  into  which  is  plunged  a  spiral  wire  of  the  same 
metal,  and,  at  the  instant  that  the  surface  of  the  bath 
solidifies,  by  aid  of  this  wire  a  cake  of  solid  platinum  is 
lifted  out  and  immersed  in  the  water-calorimeter.  Repeat- 
ing the  determination  of  this  fusing-point,  Holborn  and 
Wien  have  found  more  recently  1780°. 

The   latent  heat   of   fusion   of   platinum   is   equal   to 


GA  S-PYROMETER.  73 

74.73  c.±1.5;  this  number  results  from  five  determina- 
tions. 

2.  A  second  series  of  experiments  was  on  the  specific  heat 
of  palladium;   the  determinations  were  made,  in  part  by 
comparison  with  platinum,  in  part  by  the  air-thermometer. 
The  results  obtained  by  the  two  methods  are  concordant. 

The  mean  specific  heat  is  given  by  the  formula 

C0'  =0.0582  +D.000010  - 1. 
The  true  specific  heat  is  equal  to 

^ = 0.0582 + 0.000020  - 1. 
dt 

The  fusing-point  was  found  equal  to  1500°;  the  more 
recent  experiments  of  Holborn  and  Wien  give  1580°. 
This  difference  can  be  explained  by  impurities  in  the 
metal  and  absorption  of  furnace-gases. 

The  latent  heat  of  fusion  of  palladium,  measured  by  the 
same  experiments,  was  found  to  be  36.3  calories. 

3.  In  another  series  of  experiments  Yiolle  has  deter- 
mined the  boiling-point  of  zinc.     He  employed  an  ap- 
paratus of  enamelled  casting,  heated  in  a  triple  envelope 
of  metallic  vapor;    the  top  was  covered  with  clay  and 
cow-hair  to  prevent  superheating  of  the  coverings.     The 
measurements    were    made    with    pressure    and    volume 
simultaneously  variable. 

Volume  of  bulb 294 . 5  cc.  Volume  of  gas  let  out  184 . 3  cc. 

Waste  space 4.7  "  Pressure  892.3  mm.   7T=929°.6 

t0 3°. 8  t0.  .: 7°. 7 

H0 760 . 5  mm.  H0 759 . 5  mm. 

Bams,  Holborn  and  Wien  found  numbers  very  close  to 
930°. 


74  HIGH   TEMPERATURES. 

4.  A  last  series  is  relative  to  the  fusing-points  of  metals, 
which  were  determined  by  comparison  with  the  total  heat 
of  platinum: 

Silver 954°  (too  small  by  10°) 

Gold 1045   (  "        "  "    20  ) 

Copper 1050    (  "        "  "    15  ) 

Experiments  of  Mallard  and  Le  Chatelier. — In  their 
investigations  on  the  temperatures  of  ignition  of  gaseous 
mixtures,  Mallard  and  Le  Chatelier  made  use  of  a  porce- 
lain pyrometer,  which  was  exhausted,  then  air  was  let  in 
and  the  gaseous  volume  thus  absorbed  was  measured.  It 
is  possible  to  reach  1200°  without  noticing  any  breaking 
down  of  the  porcelain;  but  this  giving  way  is  complete 
at  1300°  under  the  action  of  the  vacuum. 

This  method  was  used  in  the  following  way  to  measure 
the  temperatures  of  ignition  of  gaseous  mixtures.  The 
air  was  exhausted  from  the  apparatus,  and  the  tempera- 
ture was  measured  by  the  air- volume  which  filled  it;  the 
air  was  again  exhausted  and  the  apparatus  was  filled  with 
the  gaseous  mixture.  Whether  or  not  there  was  ignition 
was  known  by  the  comparison  of  the  volume  of  the  mix- 
ture with  that  of  the  air  introduced  under  the  same  con- 
ditions of  temperature,  at  least  in  the  cases  of  mixtures 
burning  with  contraction. 

The  pyrometer  used  had  a  capacity  of  62  cc.,  after  de- 
duction of  the  waste  space  (1  cc.) ;  the  following  table  gives 
the  volumes  of  air  corresponding  to  different  temperatures : 

400° 26.7cc. 

600 20.6 

800 16.7 

1000 14.1 

1200.,  .  12.2 


GAS-PYROMETER. 


75 


In  admitting  that  the  measurements  of  volume  be  made 
to  0.1  cc.,  one  should  have  a  precision  of  only  10°  in  1000° 
on  account  of  the  insufficient  volume  of  the  thermometric 
reservoir. 

Experiments  of  Barns. — This  American  savant  devised 
a  rotating  apparatus,  remarkable  for  its  uniformity  of  tem- 
perature, but  he  applied  it  directly  only  to  the  standard- 
ization of  thermoelectric  couples.  He  worked  at  constant 
pressure.  By  means  of  couples  graduated  in  this  way, 
he  has  determined  the  boiling-points  of  zinc  (926°-931°) 
and  of  cadmium  (773°-784°);  the  boiling-point  of  bis- 
muth was  found  equal  to  1200°  under  a  reduced  pressure 
of  150  mm.,  which  would  give  under  atmospheric  pressure 
by  extrapolation  1500°. 

Fig.  8  represents  the  longitudinal  section  of  Barus' 
apparatus.  It  is  composed  essentially  of  a  porcelain 


FIG.  8. 

pyrometer  containing  an  interior  tube  in  which  is  placed 
the  couple.  The  pyrometer  fixed  at  a  point  of  its  stem 
is  held  stationary.  It  is  surrounded  by  a  muffle  of  casting 
whose  general  shape  is  that  of  revolution  about  the  axis 


76  HIGH  TEMPERATURES. 

of  the  pyrometer;  this  muffle  is  composed  of  two  similar 
halves  held  by  means  of  iron  collars,  and  can  be  given  a 
motion  of  rotation  about  its  axis  of  figure,  in  such  a 
manner  as  to  assure  uniformity  of  heating.  It  is  heated 
by  gas-burners  placed  below.  An  outer  covering  of  fire- 
clay keeps  in  the  heat  about  the  iron  muffle. 

Experiments  of  Holborn  and  Wien. — Holborn  and  Wien 
have  made  a  very  complete  standardization  of  the  thermo- 
electric couple  Pt — Pt-Rh  proposed  by  Le  Chatelier. 
They  made  use  of  a  porcelain  reservoir  of  about  100  cc. 
capacity,  terminating  at  its  two  ends  in  capillary  porce- 
lain tubes.  The  thermoelectric  junction  is  placed  inside 
the  bulb,  and  each  of  its  wires  is  led  out  by  one  of  the 
lateral  tubes;  this  arrangement  allows  of  determining  at 
various  points  the  real  temperature  of  the  waste  space 
whose  volume  is  1.5  cc. 

They  worked  at  constant  volume,  with  a  very  low 
initial  pressure  so  as  always  to  have  depression;  they 
were  able  to  reach  1430°.  Above  1200°  they  could  make 
but  a  single  observation  with  one  pyrometer;  below  this, 
about  ten  observations. 

They  determined  the  coefficient  of  expansion  of  their 
porcelain,  a  product  of  the  Berlin  works,  and  found  it 
equal  to  0.0000045,  the  identical  number  given  by  Le 
Chatelier  for  the  Bayeux  porcelain. 

They  made  use  of  this  pyrometer,  employing  as  inter- 
mediary a  couple,  to  fix  the  fusing-points  of  certain  metals : 

Silver 970° 

Gold 1072 

Palladium 1580 

Platinum 1780 

These  figures,  at  the  time  they  were  obtained,  were 
counted  among  those  which  seemed  to  merit  the  most 


GAS-PYROMETER.  77 

confidence;  however,  it  is  necessary  to  note  that  the 
volume  of  the  bulb  was  too  small  to  assure  a  very  great 
accuracy. 

We  shall  return  to  these  experiments  when  treating  of 
electric  pyrometers. 

Holborn  and  Day's  Investigations. — The  work  of  estab- 
lishing the  gas-scale  upon  a  satisfactory  basis  was  continued 
at  the  Reichsanstalt  by  Holborn  and  Day,  who  also  deter- 
mined the  thermo-couple  scales  in  terms  of  that  of  the 
nitrogen  constant- volume  thermometer  as  well  as  estab- 
lishing several  fixed  points. 

Their  preliminary  work  was  done  with  porcelain  bulbs 
at  temperatures  above  500°  C.  using  nitrogen  and  hydro- 
gen and  with  a  bulb  of  Jena  borosilicate  glass  No.  56m 
filled  with  hydrogen  for  temperatures  below  500°.  Por- 
celain bulbs  glazed  outside  and  also  inglazed  bulbs  were 
used.  Errors  due  to  changes  in  the  bulbs  were  detected 
by  taking  "zero"  readings  and  also  by  the  simultaneous 
use  of  thermocouples.  Salt  baths  were  used  up  to  900° 
at  first,  but  later  electric  heating  was  employed  in  all  the 
high  temperature  work. 

The  hard  glass  bulbs  of  about  167  cm.  capacity  showed 
less  changes,  after  annealing,  than  the  irregularities  in 
the  thermocouple  measurements,  due  to^the  lack  of  sen- 
sitiveness of  the  latter  at  low  temperatures;  and  these 
glass  bulbs  were  found  preferable  to  those  of  porcelain 
up  to  500°  C.  The  precision  attainable  with  thermo- 
couple control  was  about  0°.6  C. 

Porcelain  bulbs  of  100  cc.  capacity  glazed  inside  and 
out,  filled  with  hydrogen  and  heated  to  only  700°,  gave 
very  discordant  results  due  apparently  to  chemical  action 
between  the  hydrogen  and  the  walls  of  the  bulb  and  to 
water-vapor  generated.  Used  with  nitrogen  and  heated 
electrically  to  about  1100°  C.  the  mean  difference  between 


78  HIGH  TEMPERATURES. 

the  observed  and  calculated  values  was  ±  1°.5  C.  Far  less 
satisfactory  results  were  obtained  with  porcelain  glazed 
only  on  the  outside. 

A  first  series  of  experiments  with  a  metal  bulb  were 
made  with  a  20  per  cent  iridium  alloy  of  platinum,  the 
bulbs  being  cylindrical  of  208  cc.  volume  and  0.5  mm. 
wall  and  the  waste  space  was  considerably  reduced  over 
that  of  the  porcelain  bulbs.  The  electric  heating  oven 
was  also  improved  by  winding  it  logarithmically  so  that 
at  1150°  the  temperature  distribution  was  constant  to 
3°  over  that  portion  of  the  oven  containing  the  bulb. 
This  was  still  further  equalized  by  the  presence  of  the 
metallic  bulb;  also  at  very  high  temperatures  the  tend- 
ency to  equilibrium  through  radiation  balances  more 
nearly  the  losses  by  end  conduction.  Temperature  con- 
trol to  0°.l  C.  at  1000°  C.  may  be  realized  electrically  with 
care.  A  precision  of  better  than  1°  C.  was  then  obtained, 
and  the  conclusion  seemed  warranted  that  the  metallic 
bulbs  in  an  electrically-heated  furnace,  where  no  gases 
or  other  materials  acting  upon  platinum  were  in  contact 
with  it,  were  superior  to  any  form  of  porcelain  bulb. 

Their  later  work  consisted  in  a  determination  of  fixed 
points  using  the  thermocouple  as  intermediary,  after 
having  found  the  coefficient  of  expansion  of  the  material 
of  their  bulb  and  shown  that  the  bulb  underwent  no 
deformation  after  heating.  The  correction  for  expansion 
amounts  to  30°  at  1000°  and  40°  at  1150°.  The  expan- 
sion was  determined  for  a  50  cm.  bar  in  a  comparator 
which  could  be  heated  electrically  to  1000°  C. 

Although  no  change  in  volume  of  the  thin-walled  bulb 
could  be  detected  on  cooling,  a  temporary  yielding  of  the 
glowing  walls  under  the  comparatively  high  pressure 
might  have  taken  place,  so  a  bulb  having  walls  1  mm. 
thick  was  substituted,  the  composition  being  90  Pt-10  Ir. 
This  bulb  was  as  satisfactory  as  the  first. 


GAS:PYROMETER.  79 

The  results  obtained  by  Holborn  and  Day  for  the  fixed 
points,  as  well  as  their  work  with  thermo-elements,  will 
be  discussed  later. 

Experiments  of  Jacquerod  and  Perrot.  —  Only  a  pre- 
liminary publication  of  this  work  has  as  yet  been  made. 
Using  a  quartz  bulb  filled  at  constant  volume  successively 
with  nitrogen,  air,  oxygen,  carbon  monoxide,  and  carbonic 
acid,  and  employing  an  electric  resistance  furnace,  results 
agreeing  to  0°.3  were  obtained  for  the  fusing-point  of 
gold  with  the  first  four  gases  using  a  common  coefficient 
of  expansion  based  on  Chappuis  limiting  value  and  using 
varying  initial  pressures.  The  use  of  quartz  reduces  the 
correction  for  the  expansion  of  the  bulb  to  2°  at  1000°. 

This  work  shows  that  in  the  range  0-1100°  C.  the  coeffi- 
cients of  expansion  of  these  gases  are  practically  identical. 

Arrangement  of  Experiments. — The  discussion  that  we 
have  just  held  permits  us  to  define  certain  conditions  to 
which  should  conform  new  experiments  necessary  to 
further  the  accuracy  of  fusing  and  boiling  temperatures 
used  as  fixed  points  for  the  standardization  of  other 
pyrometers. 

Before  Holborn  and  Day  had  demonstrated  the  super- 
iority of  an  iridium  alloy  of  platinum  for  the  bulb,  it 
seemed  preferable  to  recommend  that  the  bulb  of  the 
thermometer  be  of  porcelain  enamelled  inside  and  out, 
as  were  the  bulbs  made  at  Sevres  for  certain  experiments 
of  Regnault  and  of  H.  Sainte-Claire-Deville.  Quartz  may 
be  found  preferable  up  to  1200°  C. 

The  capacity  of  the  bulb  should  be  as  nearly  as  may  be 
as  great  as  500  cc.,  the  condition  necessary  in  order  that 
the  error  resulting  from  the  waste  space  be  certainly  less 
than  1°. 

It  may  be  desirable  to  immerse  the  manometer  and 
other  exposed  parts  in  a  water-bath  to  insure  a  constant 
temperature. 


80  HIGH 

The  thermometric  gas  will  be  nitrogen,  or  perhaps  helium. 

The  volumenometer  method  should  be  employed,  or  any 
equivalent  method  which  does  not  suppose  the  invariability 
of  the  gaseous  mass,  and  the  greatest  changes  of  pressure 
compatible  with  the  resistance  of  the  material  will  be 
produced.  Up  to  1200°  a  high  vacuum  should  be  em- 
ployed, since  there  is  no  danger  of  deforming  the  bulb. 

Finally,  most  careful  precautions  will  be  taken  to  assure 
the  equilibrium  of  temperature  between  the  reservoir  of 
the  pyrometer  and  the  body  whose  temperature  it  is  desired 
to  measure.  Barus'  arrangement  seems  to  be  theoretically 
entirely  satisfactory,  but  it.  is  quite  complicated  and  costly. 
One  can  still  make  use  of  muffles  completely  surrounded 
with  flames,  as  in  the  fabrication  of  porcelain ;  the  tempera- 
ture there  is  very  uniform.  But  their  use  offers  a  serious 
practical  difficulty:  the  stem  of  the  pyrometer,  although 
well  protected,  frequently  breaks  at  the  point  where  it 
passes  through  the  compartment  of  flames. 

It  will  be  more  practical,  perhaps,  to  make  use  of  liquid 
baths — non-volatile  fused  salts  for  example,  kept  in  contin- 
uous agitation,  in  which  plunge  at  the  same  time  the  ther- 
mometer bulb  and  the  body  whose  temperature  is  to  be 
found,  the  heating  being  obtained  by  the  combustion  of 
gas  in  a  Perrot  furnace,  or  by  an  electric  current  passing 
through  a  coil  immersed  in  the  bath. 

If  one  has  to  use  an  ordinary  gas-furnace,  Perrot  furnace, 
or,  better,  a  Leger  furnace,  it  will  be  necessary  to  explore 
by  means  of  a  thermoelectric  couple  the  distribution  of 
temperature  in  the  whole  region  utilized. 

Satisfactory  and  uniform  heating  of  a  gas  thermometer 
at  high  temperatures  is  secured  only  by  the  immersion 
of  the  bulb  in  an  electrically  heated  furnace,  the  wind- 
ings of  which,  preferably  of  platinum  foil,  are  so  spaced 
as  to  secure  uniformity  of  temperature. 


GAS-PYROMETER. 


81 


Industrial  Air-pyrometers. — There  have  been  attempts 
to  construct  air-thermometers  suitable  for  industrial 
usage,  the  argument  sometimes  being  advanced  that 
a  gas-pyrometer  is  per  se  better  than  any  other.  As  we 
have  seen,  however,  there  is  probably  no  physical  instru- 
ment which  is  more  difficult  to  employ  satisfactorily, 
and  any  seeming  gain  in  making  direct  use  of  an  air 
thermometer  for  industrial  use  is  wholly  illusary.  Other 
evident  objections  are  fragility,  uncertain  correction  due 
to  the  waste  space,  and  the  development  of  small  and  often 
unperceived  leaks.  Furthermore  an  empirical  calibration 
is  necessary  so  that  such  an  instrument  does  not  carry  the 
gas-scale  about  with  itself. 

Among  the  instruments  that  have  been  considerably 
used  is  Wiborgh's  air-pyrometer,  shown  in  Fig.  9.  A  lens- 


shaped  V  reservoir  is  open  to  the  air  before  an  obser- 
vation is  taken,  but  when  a  temperature  is  to  be  read 
this  lens  is  closed  to  the  outer  air  and  collapsed  by  a 
lever  L,  thus  adding  a  definite  mass  of  air  to  the  bulb  V 
of  the  thermometer;  the  resulting  pressure  is  transmitted 
to  a  dial  as  in  an  aneroid  barometer;  provision  is  made 
for  automatically  correcting  for  variations  in  the  pressure 
and  temperature  of  the  atmosphere. 


82 


HIGH  TEMPERATURES. 


INDIRECT  PROCESSES. 

We  shall  place  in  this  list  various  experiments  in  which 
the  laws  of  the  expansion  of  gases  have  been  used  only  in 
an  indirect  way,  or  have  been  extended  to  vapors. 

Method  of  Crafts  and  Meier. — It  is  a  variation  of  the 
method  of  H.  Sainte-Claire-Deville  and  Troost,  consisting 
in  removing  the  gas  by  means  of  a  vacuum.  Crafts  and. 
Meier  displaced  the  gas  of  the  pyrometer  by  carbonic  acid 
or  hydrochloric  acid,  gases  easily  absorbable  by  suitable 
reagents.  Hydrochloric  acid  is  the  more  convenient,  for 
its  absorption  by  water  is  immediate;  but  there  is  to  be 
feared  at  high  temperatures  its  action  on  the  air  with 
formation  of  chlorine;  it  is  preferable  to  employ  nitrogen 
in  place  of  air. 

The  apparatus  (Fig.  10)  consists  of  a  porcelain  bulb, 
whose  inlet  is  large  enough  to  let  pass 
the  entrance-tube  of  the  gas,  which 
reaches  to  the  bottom  of  the  bulb. 
This  arrangement  increases  consider- 
ably the  influence  of  the  waste  space 
and  consequently  diminishes  the  pre- 
cision of  the  determinations. 

This  method  is  especially  conve- 
nient for  observations  on  the  densi- 
ties of  vapors  which  are  made  by  the 
same  apparatus;  it  then  allows  of 
having  an  approximate  idea  of  the 
temperatures  at  which  the  experiments 
FlG-  la  are  made. 

Crafts  and  Meier  have  in  this  way  determined  the  varia- 
tions in  density  of  iodine  vapor  as  a  function  of  the  tem- 
perature. 


CD 

[ 


GAS-PYROMETER.  83 

Regnault  had  previously  proposed  a  similar  method, 
without,  however,  making  use  of  it. 

1.  One  fills  with  hydrogen  an  iron  vessel  brought  to  the 
temperature  that  one  desires  to  measure,  and  the  hydrogen 
is  driven  out  by  a  current  of  air;    at  the  outlet  of  the 
metallic  reservoir  the  hydrogen  passes  over  a  length  of 
red-hot  copper,  and  the  water  formed  is  absorbed  in  tubes 
of   sulphuric    acid   in   puniice-stone   and   weighed.     This 
method,  very  complicated,  is  bad  on  account  of  the  per- 
meability of  the  iron  at  high  temperatures. 

At  the  same  time,  he  proposed  the  following  method: 

2.  An  iron  bottle  containing  mercury  is  taken;  the  vessel, 
being  incompletely  closed,  is  heated  to  the  desired  tem- 
perature and  then  allowed  to  cool,  and  the  remaining 
mercury  is  weighed.     This  method  is  also  defective  on 
account  of  the  permeability  of  iron  at  high  temperatures; 
the  hydrogen  of  the  furnace-gases  can  penetrate  to  the 
inside  of  the  recipient  and  drive  out  an  equivalent  quantity 
of  mercury-vapor. 

Methods  of  H.  Sainte-Claire-Deville.  —  1.  This  savant 
tried  in  the  first  place  to  measure  temperature  by  a  process 
analogous  to  that  of  Dumas'  determination  of  vapor- 
densities.  He  took  a  porcelain  bulb  full  of  air,  and  heated 
it  in  the  enclosure  whose  temperature  was  wanted,  and 
sealed  it  off  by  the  oxyhydrogen  flame.  He  measured 
the  air  remaining  by  opening  the  bulb  under  water  and 
weighing  the  water  that  entered,  or  else  he  determined 
merely  the  loss  in  weight  of  the  bulb  before  and  after 
heating. 

Observations  taken  on  the  boiling-point  of  cadmium 
gave  860°.  The  data  for  the  computation  were  as  follows : 

H  =  766.4  mm. 

Volume  of  bulb  =285  cc. 

Volume  of  remaining  air  =  72  cc. 


84  HIGH   TEMPERATURES. 

The  computation  may  be  made  also  in  this  way:  Let 
17°  be  the  surrounding  temperature;  770=273°+17°= 
290°. 

ooc 

r  =  290X^=1150°. 

The  correction  due  to  the  expansion  of  the  porcelain  is 

0.0000135X850  =  13°, 

which  gives  for  the  temperature  of  boiling  cadmium 
t=  1150°  -273°  -13°  =  864°.* 

The  figure  860°  is  too  high.  There  are  in  these  experiments 
two  possible  sources  of  error:  non-uniform  heating  on 
account  of  radiation,  and  the  possibility  of  the  existence 
of  water-vapor  in  the  bulb. 

Besides,  the  small  weight  of  the  air  and  the  difficulty  of 
closing  the  recipient  absolutely  tightly  render  the  experi- 
ments very  delicate. 

2.  In  a  second  method,  which  has  the  advantage  of 
replacing  the  air  by  a  very  heavy  vapor,  Deville  returned 
to  the  idea  of  Regnault,  consisting  in  utilizing  the  vapor 
of  mercury;  but  he  ran  against  a  practical  difficulty.  He 
had  replaced  the  permeable  iron  recipients  by  porcelain 
recipients;  the  mercury  condensed  in  the  neck  of  the 
pyrometer  and  fell  back  in  cold  drops  which  caused  the 
bulb  to  break. 

*  This  result  differs  slightly  from  that  given  by  Sainte-Claire- 
Deville,  because  we  have  taken  as  coefficient  of  expansion  of 
porcelain  the  most  recently  obtained  value;  besides,  the  assumed 
temperature  of  the  surroundings,  17°,  differs  perhaps  from  the  real 
one,  which  is  not  given. 


GAS-PYROMETER.  85 

For  this  reason  he  abandoned  mercury  and  replaced  it 
with  iodine;    the  return  of  a  cold  liquid  was  completely 
obviated  by  reason  of  the  nearness  of  the  boiling-point  of 
this  substance  (175°)  and  its  fusing-point  (113°).     A  large 
number  of  observations  were  made  by  this  method;   the 
boiling-point  of  zinc,  for  example,  was  found  to  be  equal 
to  1039°. 
The  data  were  : 

H  =758.  22  mm. 
Volume  of  bulb  ..............  "...  =277  cc. 

Increase  in  weight.     Iodine  —  air.  .  .  =  0  .  299  grm. 
Volume  of  remaining  air  ..........  =2  .  16  cc. 

Density  of  iodine-vapor  ..........  =8.  716 

The  computation  can  be  made  in  the  following  way: 

If   the   temperature   of   the   surroundings   is    17°,   the 

theoretical  weight  of  the  iodine-vapor  contained  in  the 

bulb  at  this  temperature  would  be 

27S 

1.293X8.716X0.277X^=2.92  grms. 


The  weight  of  iodine  remaining  in  the  reservoir  is, 
taking  note  of  the  correction  to  be  made  resulting  from 
the  2.16  grms.  air  which  occupy  8.9  cc.  at  930°, 

070 
0.299  +  1  .293(0.277  -  0.00216)^  =  0.634  grm. 


If  there  had  been  no  air,  the  weight  would  have  been 

277  -I-  8  Q 
0.634  X  =0.652  grm. 


=  1290°. 


86  HIGH  TEMPERATURES. 

Making  the  correction  for  the  expansion  of  porcelain 
(15°),  we  have 

T'  =  1290  -  273  -  15  =  1002°. 

The  difference  between  the  result  of  this  computation 
and  that  of  Deville  comes  from  similar  reasons  to  those 
noted  above  (page  84,  note). 

This  method  is  quite  faulty,  as  the  iodine  does  not  obey 
the  laws  of  Mariotte  and  Gay-Lussac.  The  vapor-density 
of  this  substance  decreases  with  rise  of  temperature,  this 
effect  being  attributed  to  a  doubling  of  the  iodine  mole- 
cule. This  fact  was  established  by  Crafts  and  Meier  and 
confirmed  by  Troost. 

Temperatures  .........     445°         850°       1030°       1275°       1390° 

Densities  .............  8.75        8.08  7        5.76         5.30 

~..  1         0.92        0.80        0.66         0.66 


Troost  found  5.70  at  the  temperature  of  1240°. 

If,  in  the  preceding  computation,  we  take  7.8  as  the 
density  of  iodine  at  the  boiling-point  of  zinc,  we  then  find 
a  temperature  lower  than  1*50°,  which  is  far  too  low. 

Method  of  Daniel  Berthelot.  —  All  the  preceding  methods 
are  limited  by  the  impossibility  of  realizing  solid  envelopes 
resisting  temperatures  higher  than  1500°.  D.  Berthelot 
has  devised  a  method  which,  at  least  in  theory,  may  be 
applied  to  any  temperatures,  however  high,  because  there 
is  no  envelope  for  the  gas,  or  at  least  no  envelope  at  the 
same  temperature.  It  is  based  on  the  variation  of  the 
index  of  refraction  of  gaseous  mass  heated  at  constant 
pressure;  the  velocity  of  light  depends  upon  the  chemical 
nature  and  the  density  of  this  medium,  but  is  independent 
of  its  physical  state.  A  gas,  a  liquid,  or  a  solid  of  the 


GAS-PYROMETER. 


87 


same  chemical  nature  produces  a  retardation  of  the  light 
dependent  only  upon  the  quantity  of  matter  traversed; 
this  law,  sensibly  true  for  any  bodies  whatever,  should  be 
rigorously  exact  for  substances  approaching  the  condition 
of  perfect  gases.  This  retardation  is  measured  by  the  dis- 
placement of  interference  fringes  between  two  beams  of 
parallel  light,  the  one  passing  through  the  cold  gas,  the 
other  through  the  hot  gas.  In  reality  Berthelot  employs 
a  null  method;  he  annuls  the  displacement  of  the  fringes 
in  changing  at  constant  temperature  the  pressure  of  the 
cold  gas  until  its  density  is  equal  to  that  of  the  gas  in  the 
warm  arm  which  is  at  constant  pressure. 

Apparatus. — There  is  a  difficulty  arising  from  the  neces- 
sity of  separating  the  light  into  two  parallel  beams,  then 
reuniting  them  without  imparting  a  difference  of  phase 


M> 

T 

< 

\fi/ 

i 

I 

\ 

Tl 

P 

93% 
Tl 

* 

<% 

ffl 

^ 

1 

E 

9 

FIG.  11. 

which  renders  the  fringes  invisible  with  white  light, 
is  done  in  the  following  way  (see  Fig.  11); 


This 


88  HIGH   TEMPERATURES. 

A  beam  of  light  db  falls  on  a  mirror  MM' ,  which  breaks 
it  up  into  two  parallel  beams,  bf  and  cd;  in  order  to 
separate  the  beams  so  as  to  be  able  to  place  apparatus 
conveniently  with  respect  to  them,  a  prism  P  gives  to  the 
beam  bf  the  direction  gh ;  one  can  thus  secure  a  separation 
of  92  mm.  A  second  prism  Pl  brings  the  beam  cd  into 
Im,  and  after  reflection  from  a  second  mirror,  AfjM/,  the 
fringes  are  observed  in  a  telescope  focussed  for  parallel 
rays.  The  tubes  containing  the  gases  are  placed  at  T 
and  TV 

It  is  evidently  necessary  that  the  prisms  P  and  P1  be 
perfectly  made.  A  preliminary  adjustment  is  made  with 
yellow  light,  then  it  is  perfected  with  white  light. 

The  tube  at  variable  pressure  is  closed  by  two  pieces  of 
plate  glass,  as  is  also  the  warm  tube;  these  four  plates 
should  be  absolutely  alike.  The  warm  tube  is  heated  by 
a  vapor-bath  at  low  temperatures,  by  an  electric  current 
passing  through  a  spiral  at  high  temperatures. 

But  there  is  a  difficulty  in  that 'in  the  warm  tube  there 
exists  a  region  of  variable  temperature  between  the  warm 
zone  and  the  cold  atmosphere. 

To  eliminate  the  influence  of  this  variable  zone  there  are 
inside  the  warm  tube  two  tubes  containing  running  cold 
water  whose  distance  apart  can  be  changed;  it  is  assumed 
that  the  variable  region  remains  the  same,  and  that  dis- 
tance between  the  two  tubes  gives  the  warm  column 
actually  utilized.  It  follows  that  the  comparative  lengths 
of  the  warm  column  and  of  the  cold  column  (this  latter 
remaining  constant)  are  not  the  same;  the  formula  to  be 
used  will  be  somewhat  more  complicated. 

n  being  the  index  of  refraction  of  a  gas  and  d  its  density, 
we  have 


GAS-PYROMETER.  89 

In  the  constant-pressure  tube 

d0    p9' 

To  obtain  the  invariability  of  the  fringes  it  is  necessary 
that 

(nl-n0)L=(n'-nQ)l, 

L  being  the  length  of  the  cold  tube,  and  I  the  displace- 
ment of  the  warm  tube; 

k(dl-dQ)L=k(d'-d0)l, 


T 

•i  <i 


an  expression  which  gives  a  relation  between  the  pressures 
and  the  temperatures. 

This  method,  employed  for  the  control  of  the  boiling- 
points,  has  given  the  following  results,  which  are  near  those 
calculated  from  the  old  experiments  of  Regnault: 

Temperature    Temperature 
Observed.        Calculated. 

Alcohol 741 .5  mm.  77°. 69  77°. 64 

Water 740.1  99  .2  99  .20 

"  761.04  100.01  100.01 

Aniline 746.48  183.62  183.54 

"     760.91  184.5  184.28 

Berthelot  has  standardized  by  the  same  method  a  couple 
which  he  used  to  determine  the  fusing-points  of  silver, 
copper,  gold,  and  the  boiling-point  of  zinc; 


90  HIGH   TEMPERATURES. 

Silver 962° 

Gold 1064 

Zinc 920 

Cadmium 778 

The  numbers  found  are  nearly  identical  with  those 
'which  result  from  the  best  determinations  made  by  other 
methods. 

We  shall  further  discuss  the  determinations  of  fixed 
points  in  pyrometry  in  Chapter  XIII. 


CHAPTER  IV. 
CALORIMETRIC  PYROMETRY. 

Principle.  —  A  mass  p  of  a  body,  brought  to  a  tempera. 
ture  T,  is  dropped  into  a  calorimeter  containing  water  at 
a  temperature  t0.  Let  t±  be  the  final  temperature  of  water 
and  substance.  P  being  the  water-equivalent  of  the  sub- 
stances in  contact  (water,  calorimetric  vessel,  thermometer, 
etc.)  which  are  raised  from  t0  to  tlf  L?  the  heat  required 
to  warm  unit  mass  of  the  body  from  ^  to  T,  we  have 

LTtXP=P(tl-t0). 

Taking  as  origin  of  temperatures  the  zero  of  the  centi- 
grade thermometer,  the  heat  required  to  warm  unit  mass 
of  the  body  to  the  temperature  T  will  be 


The  quantity  L0*  is  easy  to  calculate,  because  the  specific 
heats  at  low  temperatures  are  sufficiently  well  known: 


The  expression  for  the  total  heat  becomes 


*!  and  J0  are  the  temperatures  given  by  the  direct  readings 
of  the  thermometer. 

The  value  of  the  second  member  is  thus  wholly  known, 
and  consequently  that  of  the  first  member  which  is  equal 

91 


92  HIGH  TEMPERATURES. 

to  it.  If  previous  experiments  have  made  known  the  value 
of  the  total  heat  Lj  for  different  temperatures,  one  may 
from  the  knowledge  of  L%  determine  the  value  of  T.  It 
will  be  sufficient  to  trace  a  curve  on  a  large  scale  whose 
abscissas  are  temperatures,  and  ordinates  total  heats,  and 
to  find  upon  this  curve  the  point  whose  abscissa  has  the 
value  given  by  the  calorimetric  experiment. 

Choice  of  Metal. — Three  metals  have  been  proposed: 
platinum,  iron,  and  nickel. 

Platinum. — This  metal  was  first  proposed  by  Pouillet, 
and  taken  up  again  by  Violle.  It  is  much  to  be  pre- 
ferred to  the  other  metals;  its  'total  heat  has  been  com- 
pared directly  with  the  indications  of  the  air-thermometer. 
This  metal  can  probably  be  reproduced  identical  with  itself. 
Iridium,  which  commercial  platinum  often  carries,  has 
the  same  specific  heat.  The  high  price  of  these  substances 
is  an  obstacle  to  their  use  extensively  in  works ;  for  a  cal- 
orimeter of  a  liter  it  is  necessary  to  have  at  least  100 
grms.  of  platinum, — or  $100  in  a  volume  of  5  cc., — easily 
lost  or  made  away  with. 

Violle  determined  the  total  heat  of  platinum  from  0°  to 
1200°,  and  computed  by  extrapolation  up  to  1800°. 

100° 3.23  cal.       1000° 37.70  cal. 

200 6.58  1100 42.13 

300 9.75  1200  . 46.65 

400 13.64  1300 51 .35 

500 17.35  1400 56.14 

600 21 . 18  1500 61 .05 

700 25.13  1600 66.08 

800 29.20  1700 71.23 

900 33 .39  1800 76. 50 

Iron. — Regnault,  in  a  study  made  for  the  Paris  Gas 
Company,  had  proposed,  and  caused  to  be  adopted,  iron,  in 
attributing  to  it  a  specific  heat  of  0.126,  while  it  is,  at  0°, 
0.106.  He  used  a  cube  of  7  cm.  sides  which  was  thrust 


CALORIMETRIC  PYROMETRY. 


into    the   furnaces   by    means    of   long    iron   bars.    The 
calorimeter  was  of  wood  and  had  a  capacity  of  4  liters. 

Various  observers  have  determined  the  total  heat  of  iron : 
at  high  temperatures  the  accord  is  not  perfect  among  the 
results. 


Temperature 

Post 

Pionchon. 

Euchone. 

Mean 
Specific  Heat. 

Degrees. 

Calories. 

Calories. 

Calories 

Calories. 

100 

10.8 

11.0 

11.0 

10.8 

200 

22.0 

22.5 

23.0 

21.5 

300 

35.0 

36.5 

37.0 

32.5 

400 

39.5 

41.5 

42.0 

43.0 

500 

67.5 

68.5 

69.5 

54.0 

600 

86.0 

87.5 

84.0 

65.0 

700 

108.0 

111.5 

106.0 

76.0 

800 

132.0 

137  .'0 

131.0 

87.0 

900 

157.0 

157.5 

151.5 

98.0 

1000 

187.5 

179.0 

173.0 

109.0 

But  this  metal  is  not  at  all  suitable  for  such  use,  by 
reason  in  the  first  place  of  its  great  oxidability.  There  is 
formed  at  each  heating  a  coating  of  oxide  which  breaks  off 
upon  immersion  in  water,  so  that  the  mass  of  the  metal 
varies  from  one  observation  to  the  next.  Besides,  iron, 
especially  when  it  contains  carbon,  possesses  changes  of 
state  accompanied  during  the  heating  by  a  marked  absorp- 
tion of  heat.  By  cooling  in  water,  hardening  takes  place 
which  may  irregularly  prevent  the  inverse  transformations. 
The  use  of  electrolytic  iron  is  therefore  preferable. 

Nickel. — At  the  Industrial  Gas  Congress  in  1889  Le 
Chatelier  proposed  nickel,  which  is  but  slightly  oxidizable 
up  to  1000°,  and  which  above  400°  does  not  possess  changes 
of  state  as  does  iron. 

The  total  heat  of  nickel  has  been  determined  by 
Pionchon  and  by  Euchene  and  Biju-Duval. 

The  differences  are  due  very  probably  in  part  to  impuri- 
ties that  the  nickel  may  contain. 


94 


HIGH  TEMPERATURES. 


Temperature. 

Pionchon. 

Euch^ne. 

Degrees. 

Calories. 

Calories. 

100 

11.0 

12.0 

200 

22.5 

24.0 

300 

42.0 

37.0 

400 

52.0 

50.0 

500 

65.5 

63.5 

600 

78.5 

75.0 

700 

92.5 

90.0 

800 

107.0 

103.0 

900 

123.0 

117.5 

1000 

138.5 

134.0 

Calorimeters. — 1.  In  laboratories  there  is  employed  with 
the  platinum  mass  Berthelot's  calorimeter,  a  description 
of  which  is  given  in  the  Annales  de  Chemie  et  de  Physique  * 
(Fig.  12).  The  thermometer  used  for  the  measurement 


FIG.  12. 

of  the  rise  in  temperature  should  be  very  sensitive,  so 
that  a  rise  of  from  2°  to  4°  be  sufficient  in  order  to  render 

*  4th  Series,  t.  xxix.  p.  109;   5th  Series,  t.  v.  p.  5;   t.  x.  p.  433 
and  447;    t.  xn.  p.  550. 


CALOR1METRIC  PYROMETRY. 


95 


negligible  the  cooling  correction.  If  use  is  made,  for 
instance,  of  a  thermometer  giving  the  hundredth  of  a 
degree,  the  mass  of  platinum  should  be  about  one-twentieth 
the  mass  of  the  water  in  the  calorimeter. 

2.  In  the  arts,  where  the  measurements  are  made  with 
less  precision,  and  where  it  is  necessary  to  consider  the 
cost  of  installation  of  the  apparatus,  nickel  will  be  made 
use  of,  a  thermometer  giving  tenths  of  a  degree,  and  a 
zinc  calorimeter,  which  may  be  home-made.  Such  an 
installation  may  cost  as  little  as  $4.  A  mass  of  nickel 
should  be  used  equal  to  one-twentieth  of  the  mass  of 
water  of  the  calorimeter. 

The  calorimeters  used  by  the  Paris  Gas  Company  are 
after  the  Berthelot  pattern.  They  are  also  water-jacketed 
calorimeters,  of  which  there  are  two  types. 

Water- jacketed  Calorimeters  (Figs.    13   and   14). — These 


FIG.  13. 

A,  cylindrical  vessel  of  thin  copper;    B,  water-jacket;   C,  wooden 
support;    1),  handles;    E,  filling-tubes;    F,  felt  jacketing. 

apparatus  consist  of  a  cylindrical  calorimeter  of  two  liters 
capacity,  of  zinc  or  of  copper;  a  double  cylindrical  jacket 


96 


TEMPERATURES. 


of  the  same  metal,  containing  water  and  surrounded  by 
felt  on  the  outside.  The  calorimeter  rests  on  this  jacket 
by  means  of  a  wooden  support.  A  thermometer  graduated 


FIG.  14. 

A,  zinc  vessel;  B,  water-jacket;   C,  cork  supports;  E,  filling-tube; 
G,  cardboard  cover. 

to  fifths  of  a  degree,  having  a  small  but  quite  long  bulb, 
serves  as  stirrer.  The  thermometric  substance  is  a  piece 
of  nickel  of  mass  equal  to  one-tenth  that  of  the  water, 
or  200  grms.,  so  as  to  have  considerable  rise  of  tempera- 
ture easy  to  read  by  the  workmen  who  make  the  measure- 
ments. 

As  a  general  rule,  one  must  avoid  placing  the  thermo- 
metric substance'  upon  the  floor  of  the  furnace.  The 
piece  of  nickel,  which  is  made  in  the  form  of  small 
cylinders  having  from  15  to  25  mm.  diameter  and  from 
10  to  30  mm.  length,  rests  so  as  to  be  insulated  from  the 
floor  in  a  nickel  crucible  provided  with  a  foot  and  with 
two  arms  attached  somewhat  above  the 
centre  of  gravity.  When  it  has  been 
heated  for  a  half-hour  an  observer 
takes  out  the  crucible  with  a  forked 


FIG.  15. 


rod,  and  another  seizes  this  crucible  with  tongs  to  empty 
it  into  the  calorimeter. 


CALORIMETR1C  PYROMETRY. 


97 


Use  is  not  made  of  an  iron  crucible  because  this  metal 
oxidizes  and  lets  drop  scales,  which 
falling  into  the  calorimeter  would 
vitiate  the  experiment.  Fig.  15 
shows  the  arrangement  of  such  a 
crucible  containing  a  nickel  cylin- 
der. 

Siemens  Calorimeter.  —  A  con- 
venient form  of  direct-reading 
calorimeter  due  to  Siemens  is 
shown  hi  Fig.  16.  Using  always 
the  same  mass  of  water  and  a  ball 
of  given  mass  and  kind,  the  ther- 
mometer may  be  graduated  to 
read  directly  the  temperature  at- 
tained by  the  heated  ball. 

Precision  of  the  Measurements. 
— Biju-Duval  has  made  a  series  of 
experiments  to  study  the  sources 
of  error  arising  from  the  use  of 
the  calorimeter  by  comparing  its 
indications  to  those  of  the  thermo- 
electric pyrometer  of  Le  Chatelier. 
The  observations  were  taken  by 
varying  the  following  conditions: 

Use  of  thermometer  graduated 
to  Y5°  or  to  V^0. 

Use  of  the  old  wooden  gas- 
works calorimeter  or  of  the  water- 
jacketed  calorimeter. 

Use  of  iron  or  nickel. 

I.  Experiment.  —  Old  wooden 
gas-works  calorimeter.  Iron. 
Thermometer  in  fifths. 


PIG.  16. 


98  HIGH  TEMPERATURES. 

P=  10000  grm. 
7)  =    1031    " 


Q</=  153.5  cal. 

Computed  temperature: 

Mean  specific  heat  of  iron  =  0.108      t  =  1420° 
"     "    "    =0.126      *  =  1210 
Total  heat  according  to  Biju-Duval  =  915 
Thermoelectric  pyrometer  =   970 

It  is  thus  evident  that  the  mean  specific  heats  even 
with  the  correction  suggested  by  Regnault  give  tempera- 
tures much  too  high.  With  the  curve  of  total  heats  the 
temperature  found  is  much  too  low  on  account  of  the 
following  losses  of  heat: 

1.  Absorption  of  heat  by  the  wooden  walls; 

2.  Radiation  from  the  iron  cube  during  transfer; 

3.  Cooling  of  the  water  in  the  .calorimeter,  whose  tem- 
perature exceeded  by  16°  the  temperature  of  the  surround- 
ings. 

The  following  experiments  were  made  with  the  ther- 
mometer reading  to  l/so° ;  the  piece  of  nickel  was  protected 
against  radiation  by  a  crucible.  The  two  calorimeters  were 
compared. 

II.  Trial  ivith  the  Wooden  Calorimeter. 

r=975°  by  the  thermoelectric  pyrometer 

P  =  10000  grm. 

p  =  145 

*0=20°.21 

*t=21°.99 
if«125cal. 
I    =  130  cal.  from  the  curve  at  975° 


CALORIMETRIC  PYROMETRY.  99 

The  difference  is  5  calories,  or  4  per  cent  loss  due  to  the 
jacket. 

III.  Trial  with  the  Water-  jacketed  Calorimeter. 


P=2000grm. 
p=48.4     " 


£1?*=  131.5  cal.  from  the  curve  at  985° 

The  difference  is  1.5  calories,  or  a  loss  of  only  1.11  per 
cent  when  use  is  made  of  a  carefully  made  calorimeter  and 
of  a  thermometer  giving  1/50°.  This  corresponds  to  an 
uncertainty  of  less  than  10°  in  the  temperatures  sought. 
With  the  yio°  thermometers,  necessitating  a  much  greater 
rise  of  temperature  of  the  water  in  the  calorimeter,  an 
uncertainty  of  25°  will  exist. 

Conditions  of  Use.  —  The  advantages  of  the  calorimetric 
pyrometer  are: 

1.  Its  low  net  cost; 

2.  The  ease  of  its  use,  which  allows  of  putting  it  in  the 
hands  of  a  workman. 

Its  inconveniences  are: 

1.  The  time  necessary  to  take  an  observation,  about  a 
half  -hour;    except  with  Siemens  form. 

2.  The  impossibility  of  taking  continuous  observations. 

3.  The  impossibility  of  exceeding  1000°  by  the  use  of 
the  piece  of  nickel. 

4.  The  deterioration  of  the  balls  used  due  to  oxidation. 
Its  use  does  not  seem  to  be  recommendable  for  labora- 

tories. 
It  is  to  be  recommended  for  works  in  the  cases  where  it 


100  HIG:i   TEMPERATURES. 

is  required  to  make  only  occasional  measurements ;  in  cases 
where  there  is  not  the  personnel  sufficiently  skilful  to  use 
the  more  precise  methods ;  and  finally  where  the  importance 
of  the  measurements  is  not  such  as  to  justify  the  buying 
of  more  costly  instruments. 


CHAPTER  V. 
ELECTRICAL  RESISTANCE  PYROMETER. 

Principle. — In  this  apparatus  use  is  made  of  the  varia- 
tions of  electric  resistance  of  a  platinum  wire  as  a  function 
of  the  temperature;  these  variations  are  of  the  order  of 
magnitude  of  those  of  the  expansion  of  gases.  The  ratio 
of  the  resistances  is  1.34  at  100°,  and  4  at  1000°.  As  elec- 
tric resistances  are  measurable  with  great  accuracy,  this 
process  of  estimation  of  temperatures  offers  a  very  great 
sensibility,  and  applying  exactly  the  law  that  connects  the 
variations  of  resistances  to  those  of  temperature  most 
excellent  results  may  be  obtained. 

The  electric  pyrometer  was  proposed  by  Siemens  in  1871 
(Bakerian  Lecture);  it  rapidly  came  into  use  in  metal- 
lurgical works  on  account  of  the  reputation  of  its  inventor, 
but  it  was  soon  abandoned  for  reasons  which  will  be  given 
later. 

Investigations  of  Siemens. —  The  Siemens  pyrometer 
consists  of  a  fine  platinum  wire  1  m.  long  and  0.1  mm.  in 
diameter,  wound  on  a  cylinder  of  porcelain  or  fire-clay ; 
the  whole  is  enclosed  in  an  iron  tube,  destined  to  protect 
the  instrument  from  the  action  of  the  flames. 

Siemens  tried  also,  but  without  success,  ceramic  matters 
impregnated  with  metals  of  the  platinum  group. 

To  measure  resistance  he  employed  either  a  galvanom- 
eter, for  laboratory  experiments,  or  a  voltameter,  for  the 
measurement  in  works.  In  this  latter  case  the  current 
from  a  cell  divides  between  the  heated  resistance  and  a 

101 


102  HIGH   TEMPERATURES. 

standard  resistance  at  constant  temperature;  in  each  one 
of  the  circuits  was  placed  a  voltameter:  the  ratio  of  the 
volumes  of  gas  set  free  gives  the  ratio  of  the  current 
strengths  and  thus  the  inverse  ratio  of  the  resistances. 

Finally  Siemens  gave  a  formula  of  three  terms  connect- 
ing the  electrical  resistance  of  platinum  to  temperatures 
on  the  air-thermometer,  but  without  publishing  the  ex- 
perimental data  on  which  this  graduation  was  based. 

Experiment  soon  showed  that  the  apparatus  did  not  rest 
comparable  with  itself.  A  committee  of  the  British 
Association  for  the  Advancement  of  Science  found  that  the 
resistance  of  platinum  increases  after  heating.  It  would 
be  necessary  then  to  graduate  the  apparatus  each  time  that 
it  was  used.  This  change  of  resistance  is  due  to  a  chemical 
alteration  of  platinum,  which  is  enormous  when  directly 
heated  in  the  flame,  less,  but  still  marked,  if  placed  in  an 
iron  tube,  and  which  disappears  if  use  is  made  of  a 
platinum  or  porcelain  tube.  This  augmentation  of  resist- 
ance may  reach  15  per  cent  by  repeated  heatings  up  to 
900°. 

Platinum  being  very  costly  and  porcelain  very  fragile,  it 
was  impossible  to  use  these  two  bodies  in  the  industries, 
which  alone  at  that  time  occupied  themselves  with  meas- 
urements of  high  temperatures,  and  this  method  was 
abandoned  completely  during  twenty  years. 

Researches  of  Callendar  and  Griffiths. — These  savants 
have  revived  this  method  for  laboratory  purposes;  it 
seems  the  best  for  work  of  precision,  on  the  condition  of 
being  assured  of  the  invariability  of  the  resistance  of 
platinum. 

Callendar  found  that  clay  helps  to  cause  the  variation 
of  resistance,  that  the  platinum  wire  becomes  brittle  on  its 
support  and  sticks  there;  this  action  is  probably  due  to 
impurities  in  the  clay.  With  mica,  on  the  other  hand, 
which  the  wire  touches  only  at  the  edges  (the  reel  is  made 


ELECTRICAL  RESISTANCE  PYROMETER.        103 

of  two  perpendicular  slices  of  mica),  there  is  perfect  in- 
sulation without  cause  of  alteration;  but  mica  becomes 
dehydrated  at  800°  and  then  becomes  very  fragile. 

All  metallic  solderings  should  be  proscribed,  for  they  are 
volatile  and  attack  platinum. 

Pressure  joints  (screw  or  torsion)  are  equally  bad,  for 
they  become  loose.  One  should  use  only  the  "autogene" 
solder  by  the  fusion  of  platinum. 

Copper  conductors  should  also  be  rejected,  at  least  hi 
the  heated  portions,  on  account  of  the  volatility  of  the  metal. 
A  pyrometer  with  such  conductors,  .heated  during  an  hour 
at  850°,  showed  an  increase  of  resistance  of  J  per  cent. 

Investigations  of  Holborn  and  Wien. — These  savants 
have  made  a  very  complete  study  of  this  alterability  of 
platinum  wires,  in  a  comparison  between  the  methods  of 
measurement  of  temperatures  by  electric  resistance  and 
thermoelectric  forces;  they  worked  with  wires  of  0.1  mm.  to 
0.3  mm.  diameter.  They  soon  found  that  above  1200° 
platinum  commences  to  undergo  a  feeble  volatilization 
which  suffices  to  augment  notably  the  resistance  of  the 
very  fine  wires.  Hydrogen  in  presence  of  silicious  matters 
causes  at  about  850°  a  rapid  alteration  of  the  platinum. 

Below  are  the  results  relative  to  wires  of  0.3  mm.  of  a 
length  of  160  mm. 

Wire  a.  R  at  15°.  Wire  ft.  R  at  15°. 

At  start 0 . 239  ohm  At  start. 0 . 247  ohm 

After  heating  red-hot :  After  several  days  in  )  (( 

Twice  in  air  at  1200°  0 . 238    "  hydrogen  at  15°    f 

Onceinvacuo      "      0.240    "  After  heating  in  hy- 


H            "      0.262   "  drogen  to  1200°    '  °'255 
"   vacuo      "      0.253    " 

Wire  r-  R  at  15°. 

At  start 0. 183  ohm 

After  heating  in  air  to  1250°  (three  times)  0.182    " 

"         "        "  H   "        "  0.188    " 

«        «        «   «   u       ft  ^  Q.195   " 


104  HIGH   TEMPERATURES. 

Wire  ;-  heated  to  1350°  in  an  earthenware  tube  and  in 
hydrogen  became  brittle;  this  result  may  be  explained  by 
a  siliciuration  of  the  platinum,  for  there  is  nothing 
observed  if  the  wire  is  heated  by  the  electric  current  in  the 
interior  of  a  cold  glass  tube,  even  in  hydrogen.  Similar 
experiments  were  made  by  the  same  observers  with  palla- 
dium, rhodium,  and  iridium. 

With  palladium  the  absorption  of  hydrogen  at  low  tem- 
peratures, giving  the  hydride,  increases  the  resistance  by 
60  per  cent;  besides,  the  same  effect  of  alteration  as  with 
platinum  is  noticed  if  the  palladium  is  placed  in  hydrogen 
in  presence  of  silicon. 

There  is  no  definite  conclusion  to  be  drawn  from  the 
experiments  with  rhodium  and  iridium,  except  that  these 
metals  assume  their  normal  resistance  only  after  having 
been  heated  several  times  to  a  high  temperature. 

Law  of  the  Variation  of  Platinum  Resistance.  —  Cal- 
lendar  and  Griffiths  have  compared  the  resistance  of 
platinum  with  the  air-thermometer  up  to  550°;.  they  found 
that  up  to  500°  the  relation  could  be  represented  at  least 
to  0°.l  by  a  parabolic  formula  of  three  parameters.  In 
order  to  graduate  such  a  pyrometer  it  would  be  sufficient 
then  to  have  three  fixed  points:  ice,  water,  sulphur. 

They  gave  a  special  form  to  the  relation;  let  p  be  the 
electric  temperature  defined  by  the  relation 


that  is  to  say,  the  value  of  the  temperature  in  the  case  in 
which  the  resistance  varies  proportionally  to  the  tempera- 
ture. 

They  then  placed 


* 'Pt — "  t  f\f\     I      I  t  f\r, 


ELECTRICAL  RESISTANCE  PYROMETER.        105 

It  would  appear  as  if  this  formula  contained  the  single 
parameter  d;  but  in  reality  pt  includes  two. 
Substituting  for  p  its  value,  we  have 


_P/  I 


(100)2  (100) 

an  equation  of  the  form 


This  complicated  form  is  without  interest.  Callendar 
and  Griffiths  used  their  pyrometer  before  having  standard- 
ized it  against  the  air-thtrmometer.  Not  being  able  to 
compute  t,  they  provisionally  computed  the  approximate 
temperatures  pt,  and  later  determined  the  correction 
between  t  and  pt,  after  having  sought  the  formula  express- 
ing the  difference  between  these  two  quantities.  By  extra- 
polation up  to  1000°  the  points  of  fusion  of  gold  and  of 
silver  were  found  quite  near  to  those  determined  by  other 
observers. 

Harker,  working  at  the  National  Physical  Laboratory, 
England,  has  recently  compared  the  readings  of  platinum- 
thermometers,  when  reduced  to  the  air-scale  by  the  use  of 
Callendar's  difference  formula,  with  the  readings  of  thermo- 
couples calibrated  at  the  Reichsanstalt,  and  with  the 
indications  of  an  inglazed  porcelain-bulb  nitrogen-thermom- 
eter at  contant  volume.  Specially  constructed,  compen- 
sated electric  furnaces  were  used  for  heating. 

As  shown  by  the  table  on  p.  106,  the  agreement  between 
the  scales  of  the  platinum-resistance  and  thermoelectric 
pyrometers  was  within  0°.5  C.  throughout  the  temperature 
range  up  to  1000°,  although  the  gas-pyrometer  gave  some- 
what discordant  results. 


106 


HIGH  TEMPERATURES. 


COMPARISONS    OF    PYROMETRIC    SCALES. 


Temperature. 

G  —  Pt. 

G—  Th. 

P  —  Th. 

Gas-ther- 

Thermo- 

Pt Ther- 

mometer. 

couple. 

mometer. 

523.1 

524.3 

524.39 

-1.3 

-1.2 

-0.1 

598.5 

597.8 

597  .  62 

+  0.9 

+  0.7 

-0.2 

641.1 

641.1 

641.75 

+  0.6 

+  0.0 

-0.6 

776.7 

775.5 

775.13 

+  1.6 

+  1.2 

-0.4 

820.0 

818.4 

818.31 

+  1.7 

+  1.6 

-0.1 

875.0 

875.4 

875.24 

-0.2 

-0.4 

-0.2 

959.8 

956.0 

955.47 

+  4.3 

+  3.8 

-0.5 

1005.0 

1004.4 

1004.37 

+  0.6 

+  0.6 

-0.0 

These  results  confirm  the  view  of  the  sufficiency  of  the 
difference  formula  for  the  most  accurate  work  up  to  the 
upper  limit  of  the  safe  use  of  the  platinum-resistance 
thermometer. 

Holborn  and  Wien  have  shown-  that  at  very  high  tem- 
peratures the  interpolation  formula  is  certainly  inexact. 
The  resistance  seems  to  become  asymptotic  to  a  straight 
line,  while  the  formula  leads  to  a  maximum  evidently 
inacceptable  ;  it  would  be  without  doubt  better  represented 
by  an  expression  of  the  form 


Here  are  the  results  of  several  experiments  made  on 
the  same  wire  by  these  two  savants: 


t.  R. 

Degrees.  Ohms. 

0 0.0355 

1045 1510 

1193 1595 

1303 1699 

1395 1787 

1513 1877 

1578..  .1933 


t.  R. 

Degrees.  Ohms. 

0 0.0356 

1040 1487 

1144 1574 

1328 1720 

1425 1802 

1550 1908 

1610..  .1962 


ELECTRICAL  RESISTANCE  PYROMETER.        107 

This  wire  came  in  contact  with  the  furnace-gases,  as 
a  result  of  breaking  the  tube,  and  was  broken.  Another 
wire  gave  the  following  results : 

t.  R. 

567° 0.0972  at 

772 1164 

1045 1408 

1185 1511 

1263 1573 

Although  the  work  of  Holborn  and  Wien,  as  well  as 
that  of  Tory  and  others,  shows  that  the  platinum-resist- 
ance thermometer  cannot  be  depended  upon  above  1000°  C., 
yet,  in  the  range  from  -200°C.  to  +1000°C.,  it  serves 
as  the  most  accurate,  and,  on  the  whole,  most  convenient 
method  of  measuring  temperatures  where  great  precision 
is  required,  and  is  particularly  adapted  for  the  delicate 
control  of  a  given  temperature. 

Nomenclature. — To  determine  a  temperature  by  means 
of  a  platinum-thermometer,  if  the  instrument  has  not 
been  calibrated  already  in  degrees,  it  is  necessary  to  know 
the  difference  coefficient  d  of  the  wire,  which  may  be 
obtained  by  finding  the  platinum  temperature  pt  at  some 
known  point  as  the  sulphur  boiling-point  (S.B.P.),  or 
by  comparison  with  a  calibrated  instrument. 

Callendar  has  suggested  the  following  notation  which 
seems  convenient  for  platinum  thermometry: 

Fundamental  Interval. — The  denominator  Rm—R0  in  the 
formula 

Pt=m(R-R0)/(R™-Ro),.    •   .   .   (i) 

for  the  platinum  temperature  pt,  represents  the  change  of 
resistance  of  the  thermometer  between  0°  and  100°. 
Fundamental    Coefficient =c=mean    value    of    tempera- 


108  HIGH   TEMPERATURES. 

ture  coefficient  of  change  of  resistance  between  0°  and 
100°: 


Fundamental  Zero=pt0=-  =  reciprocal  of  fundamental 

0 

coefficient.     It  represents  the  temperature  on  the  scale  of 
the  instrument  itself  at  which  its  resistance  would  vanish. 
Difference  Formula.  —  The  following  form  is  the  most 
convenient  for  computation: 

D=t-pt  =  d-(t/m-l)-t/m.  ...     (2) 

Parabolic  Function  expresses  the  vanishing  at  0°  and 
100°  of  above  formula,  which  becomes 


"S.B.P."  Method  of  Reduction.—  D  is  obtained  very 
conveniently  by  determining  R",  and  thus  pt"  at  £"=the 
boiling-point  of  sulphur. 

Resistance  Formula.  —  The  parabolic  difference  formula 
is  equivalent  to  assuming 


.....     (3) 

where 


Graphic  Method  of  Reduction.  —  The  easiest  way  to 
reduce  platinum  temperatures  to  the  gas-scale  is  to  plot 
the  difference  t  —  pt  in  terms  of  t  as  abscissas,  and  to 
deduce  graphically  the  curve  of  difference  in  terms  of  pt 
as  abscissas.  This  is  most  convenient  for  a  single  instru- 
ment up  to  500°. 


ELECTRICAL  RESISTANCE  PYROMETER.      109 

Other  methods  have  been  used  by  Heycock  and  Neville 
and  by  Tory. 

Difference  Formula  in  Terms  of  pt: 

t-pt  =  d'(pt/lQQ-l)pt/lQO=d'p(pt).    .     .     (4) 

This  formula  is  to  be  used  only  where  a  high  degree  of 
accuracy  is  not  required.  The  value  of  df  may  be  deter- 
mined from  S.B.P.,  or  approximately 

d'  =  fl/(  1-0.0773). 
Dickson  has  proposed  the  formula 


which  agrees  with  (3)  over  a  very  wide  range  in  the  case 
of  platinum.  It  has  the  possible  theoretical  advantage  of 
not  requiring  a  maximum  value  for  the  resistance  of 
platinum.  This  form,  however,  does  not  lend  itself  to  the 
convenient  graphical  treatment  applicable  to  the  difference 
formula. 

There  is  advantage  in  using  the  silver  fusing-point  in 
calculating  the  value  d  for  impure  wires  that  are  to  be  used 
at  high  temperatures.  For  the  whole  range  of  tempera- 
tures with  such  a  wire  both  the  sulphur  and  silver  points 
may  be  obtained,  when  d  takes  the  form  a  +  bt. 

The  platinum-thermometer  may  be,  and  should  be,  for 
practical  work,  constructed  so  as  to  read  directly  in  platinum 
degrees.  This  method  saves  much  time  and  chance  of 
error.  The  calibration  curve  once  made  for  a  given  instru- 
ment serves  indefinitely,  so  that,  in  spite  of  the  appearance 
of  complications  in  the  method,  actually  in  practical  use 
the  determination  of  a  temperature  on  the  normal  scale 
by  the  platinum-thermometer  is  the  affair  of  a  few  seconds 
only. 


110  HIGH  TEMPERATURES. 

Use  as  a  Standard. — A  very  careful  comparison  of  the 
reduced  indications  of  several  platinum-thermometers  with 
the  gas-scale  as  furnished  by  a  constant- volume  nitrogen- 
thermometer  has  been  made  recently  by  Chappuis  and 
Barker  at  the  International  Bureau  at  Sevres,  and  their 
results  confirm  those  of  Callendar:  that  the  indications  of 
the  platinum-thermometer  up  to  600°  C.  can  be  sufficiently 
well  expressed  by  Callendar 's  formula. 

In  view  of  the  relative  ease  and  great  precision  of  the 
resistance  measurements  and  the  great  difficulties  in  the 
use  of  the  gas-thermometer,  Callendar  has  suggested  that 
the  platinum-thermometer  be  adopted  as  a  secondary 
standard,  reducing  its  readings  as  above  indicated,  assum- 
ing as  calibration-points  0°,  100°,  444°. 5,  the  last  being 
the  sulphur  boiling-point  on  the  constant-pressure  scale. 
All  platinum-thermometers  could  then  be  compared  with 
one  selected  as  standard  and  calibrated  as  above  indi- 
cated. With  regard  to  portability  and  ease  of  reproduc- 
tion, it  is  sufficient  to  send  a  few  grammes  of  the  standard 
wire  in  an  ordinary  letter,  to  reproduce  the  scale  with  the 
utmost  accuracy  in  any  part  of  the  world. 

Experimental  Arrangements  (Fig.  17). — In  Callendar 's 
pyrometer  the  platinum  wire  is  wound  on  two  strips  of 

Porcelain  Ttfbe  1j 


FIG.  17. 

mica  set  crosswise.  Four  heavy  platinum  wires  serve  to 
lead  in  and  out  the  current ;  two  of  them  are  to  compensate 
for  the  influence  of  temperature  along  the  parallel  con- 
ductors. 


ELECTRICAL  RESISTANCE  PYROMETER.        Ill 

In  the  laboratory  the  resistance  measurements  are  made 
by  a  Wheatstone  bridge  (Fig.  18).  A  resistance-box  is 
used,  furnished  also  with  a  rheostat  consisting  of  a  stretched 
platinum  wire  serving  to  measure  the  small  fractions  of 
resistance. 

In  industrial  practice  use  is  made  of  an  apparatus  (Fig. 
19)  composed  of  a  needle-galvanometer  and  a  resistance- 


(9)    fg)    0 


BIO 

LJLLULLJ 

L    I 

l_t_I_LJLJUei3 

EsL 

X 

~C?  —  -- 

I<H 

FIG.  18. 


O      O 


40M60?fl 


FIG.  19. 

box  of  circular  form,  consisting  of  fifteen  spools  of  1  ohm. 
The  deflection  corresponding  to  two  successive  contacts  is 
read,  and  by  interpolation  is  found  the  real  value  of  the 
resistance.  The  approximation  thus  obtained  is  sufficient. 


112 


man  TEMPERATURES. 


Another  form  of  direct-reading  instrument,  designed  by  Mr. 
Whipple  of  the  Cambridge  Scientific  Instrument  Co.,  is 
shown  in  Fig.  20.  This  instrument  is  portable,  direct-read- 
ing, and  requires  no  especial  skill  to  use  it. 


FIG.  20. 

To  avoid  breaking,  the  pyrometer  should  be  installed 
in  advance  in  the  cold  furnace,  or  heated  previously  in  a 
muffle  if  it  is  necessary  to  introduce  it  into  the  hot  fur- 
nace. It  is  necessary  to  take  care  and  heat  the  porcelain 
throughout  sufficient  of  its  length  in  order  to  avoid  the 
effect  of  the  interior  conductibility,  which  would  prevent 
the  spiral  taking  the  temperature  of  the  surrounding 
medium. 

Some  Results  Obtained. — Callendar  and  Griffiths  have 
determined  a  certain  number  of  fusing-  and  boiling-points : 


Fusion. 

Tin 232° 

Bismuth 270 

Cadmium 322 

Lead 329 

Zinc.  .  .  421 


Ebullition  under  760  mm. 

Aniline 184°.  1 

Naphthaline 217  .8 

Benzophenone  ....   305  .8 

Mercury 356  . 7 

Sulphur 444  .5 


ELECTRICAL  RESISTANCE  PYROMETER.      113 


We  may  compare  these  results  with  the  anterior  deter- 
minations of  Crafts  with  the  air-thermometer: 


Naphthaline. 


P- 
Millimeters. 

730.3 
740.3 
750.5 
760.7 


t. 

Degrees. 

216.3 
216.9 
217.5 
218 


Benzophenone. 

V.  t. 

Degrees. 

304.2 
304.8 
305.5 
306.1 


Millimeters. 

730.9 
740.1 
750.9 
760.3 


Regnault  had  found  for  mercury: 

t= 350°  under  a  pressure  of 663     mm. 

i=360        "     "        "        " 797.7   " 

£=370        "     "        "        " 954.6" 

Heycock  and  Neville  have  applied  the  method  pre- 
viously described,  in  prolonging  the  graduations,  by  extra- 
polation, to  the  determination  of  the  f  using-points  of  several 
metals  and  salts: 

Tin 232° . 

Zinc 419 

Magnesium  (1  per  100  of  impurities) . . .     633 

*1™1^-  —     629'5 

Aluminium  (0.5  per  100  of  impurities)  .     654 . 5 

Silver 960. 5 

Gold 1062 

Copper 1080. 5 

c  1084°  (fusion) 
Potassium  sulphate j  ^    (solidification) 

Sodium  sulphate j    9°2   <» 

(    883    (solidification) 

Sodium  carbonate.  ......       850 

The  difference  found  between  the  points  of  fusion  and 
of  solidification  of  potassium  sulphate  is  explained  by  the 
presence  of  a  dimorphic  point  of  transition  in  the  neigh- 
borhood of  the  fusing-point.  It  is  a  case  analogous  to  that 


114  HIGH   TEMPERATURES. 

of  sulphur;  there  is  observed,  according  to  the  case,  the 
point  of  fusion  or  solidification  of  the  one  or  the  other 
dimorphic  variety.  It  is  without  doubt  the  same  in  the 
case  of  the  sodium  sulphate. 

Sources  of  Error. — Heating  of  Thermometers  by  the  Meas- 
uring Current. — It  is  evident  that  if  a  too  large  current  is 
sent  through  an  electrical-resistance  thermometer,  the  heat- 
ing thus  occasioned  will  cause  the  indicated  temperatures  to 
be  high.  The  limiting  value  of  the  current  Callendar  has 
shown  to  be  about  0.01  ampere  per  0.01  degree  with  an 
average  platinum-thermometer  of  wire  0.15  mm.  in  diam- 
eter. If  a  galvanometer  of  sufficient  sensibility  is  used 
this  effect  is  negligible,  and  when  a  greater  current  has  to 
be  used  on  account  of  lack  of  galvanometer  sensibility, 
the  heating  effect  may  be  maintained  nearly  constant 
by  keeping  the  current  constant  by  means  of  a  rheostat 
in  the  battery  circuit,  since  the  resistance  of  the  ther- 
mometer increases  very  nearly  as  fast  as  the  rate  of  cooling, 
or  a-  little  faster  than  the  temperature.  Callendar  also 
indicates  that  the  heating  effect "  is  readily  measured  by 
using  as  current-source  two  storage  cells,  connected  first 
in  parallel  and  then  in  series,  the  current  heating  correc- 
tion being  given  by  subtracting  from  the  first  reading 
one-third  of  the  difference  between  the  two  readings. 

Lag  of  the  Platinum-thermometer.  —  Enclosed  as  it 
necessarily  is  for  most  work  in  a  sheath  of  porcelain  and 
possessing  besides  considerable  mass,  the  platinum- ther- 
mometer does  not  immediately  assume  the  temperature 
of  its  surroundings.  Put  into  a  sulphur  bath  it  assumes 
an  equilibrium  condition  in  ten  minutes.  For  small 
changes  of  temperature  this  effect  is  hardly  perceptible 
and  may  be  neglected  in  all  practical  work. 

Insulation. — Defective  insulation  due  to  moisture  con- 
densed in  the  tubes  is  sometimes  a  source  of  error  in 


ELECTRICAL  RESISTANCE  PYROMETER.        115 

accurate  work  at  the  ice  point  and  lower  temperatures 
with  thermometers  of  high  resistance  if  the  tubes  are  not 
sealed.  This  may  be  readily  done  if  the  containing 
sheath  is  of  glass,  by  sealing  the  platinum  leads  into  the 
glass  so  that  they  terminate  in  cups.  When  the  contain- 
ing sheath  is  of  porcelain,  as  for  high  temperature  work, 
this  sealing  is  not  necessary,  nor  is  it  possible,  but  running 
the  leads  into  metal  cups  containing  a  fusible  alloy  still 
offers  the  readiest  method  of  securing  a  good  contact 
with  the  rest  of  the  circuit. 

Compensation  for  Resistance  of  the  Leads. — It  is  neces- 
sary, in  order  to  avoid  thermal  currents  at  the  junctions 
with  the  thermometer  proper  and  also  evaporation  and 
consequent  change  of  resistance,  to  employ  platinum 
leads  from  the  thermometer  to  a  .point  in  the  circuit  at 
a  constant  temperature.  These  leads  should  be  of  rela- 
tively large  size  to  keep  their  resistance  as  small  as  pos- 
sible, but  even  then  there  will  still  remain  an  error  due 
to  the  varying  resistance  of  these  leads  with  change  in 
temperature  and  with  varying  depth  of  immersion.  It 
becomes  necessary  either  to  apply  a  "stem  correction," 
which  is  troublesome  and  uncertain,  or  compensate  for 
this  effect.  Nowadays  most  platinum-thermometers  sold 
are  compensated. 

This  compensation  is  effected  in  either  of  two  ways; 
in  the  first,  when  the  platinum-thermometer  PT  forms  one 
arm  of  a  Wheatstone  bridge  (Fig.  21),  the  compensating 
leads  A  VB2J  of  exactly  the  diameter  and  resistance  of  the 
thermometer  leads  CJO^  are  inserted  in  the  balancing  arm 
R  of  the  bridge,  so  that  the  resistance  of  the  thermometer 
remains  apparently  constant  for  any  depth  of  immersion. 

The  second  method  of  compensation  is  employed  when 
the  resistance  of  the  thermometer  is  to  be  determined 
by  means  of  a  potentiometer  and  standard  resistance 


116 


HIGH   TEMPERATURES. 


(Fig.  22).  Potential  leads,  which  may  be  of  fine  wire, 
are  soldered  to  the  terminals  of  the  thermometer,  and 
the  measuring  current  being  kept  constant,  the  P.D. 
across  the  standard  resistance  and  across  the  thermometer- 
coil  are  measured  rapidly  in  succession  by  means  of  a 


Bridge  wire 

uU 

( 

T) 

A! 

°, 

15, 

D! 

PT. 
FIG.  21. 

potentiometer  (Fig.  23), thus  giving  directly  the  resistance  of 
the  thermometer-coil  alone  in  terms  of  the  standard  resist- 
ance.     Either  of  these  methods  of  compensation  and  of 
resistance  measurement  is  susceptible  of  great  accuracy. 
Pyrometers  having  Different  Values  of  d. — The  value  of 


ELECTRICAL  RESISTANCE  PYROMETER.         117 


118 


HIGH   TEMPERATURES. 


<?is  a  measure  of  the  Chemical  properties  alone  of  the  plati- 
num wire  used,  the  pure  metal  having  a  value  of  very 
exactly  d=  1.500  and  impure  metals  giving  greater  values. 
It  might  be  expected  that  thermometers  having  very 
different  values  of  d  would  give  discordant  results  when 
reduced  by  the  parabolic  formula  to  the  gas-scale.  The 
work  of  Heycock  and  Neville  shows,  however,  that  such  is 
not  the  case,  as  is  indicated  by  the  following  observations 
on  the  freezing-point  of  gold: 


Pyrometer. 

d 

pt 

t°C. 

13 

1.500 

908.60 

1061.8 

16 

1.532 

906.56 

1062.1 

13A 

1.553 

905.8 

1061.9 

15 

2.04 

873.1 

1061.2 

Wires  having  a  large  d  are  more  liable  to  change  with 
use,  so  that  although  correct  results  may  be  obtained 
with  them  if  checked  up  occasionally,  it  is  preferable 
to  use  the  purest  of  platinum. 

Changes  in  the  Constants. — If  platinum-thermometers 
are  repeatedly  heated  to  temperatures  in  the  neighbor- 
hood of  1000°  C.,  or  are  kept  for  very  considerable  periods 
of  time  at  even  lower  temperatures,  changes  in  the  value 
of  the  constants  R0,  Rm,  and  d  will  develop.  Pyrometers 
for  use  at  high  temperatures  should  not  be  enclosed  in 
inglazed  porcelain  even  if  the  glaze  does  not  touch  the 
metal,  as  deterioration  of  the  latter  will  otherwise  ensue. 
The  mica  supports  undergo  distortion  on  cooling  from 
high  temperatures,  increasing  in  size,  tending  to  stretch 
the  wire  and  increase  its  resistance.  For  this  reason  it  is 
probably  better  to  use  the  constants  determined  before 
a  measurement  at  high  temperature  rather  than  those 


ELECTRICAL  RESISTANCE  PYROMETER.        119 

determined  afterwards.  Again,  if  the  wire  of  the  ther- 
mometer has  not  been  well  annealed  at  a  temperature 
higher  than  it  is  to  be  used,  irregular  changes  will  occur 
which  are  the  most  marked  for  the  first  few  heatings. 

Conditions  of  Use. — The  electrical-resistance  pyrometer 
seems,  by  reason  of  the  great  precision  of  the  measure- 
ments which  it  allows,  to  be  especially  serviceable  for 
laboratory  investigations.  It  seems,  on  the  other  hand,  to 
be  too  fragile  for  the  greater  part  of  the  industrial  appli- 
cations, although  it  is  very  convenient  in  permanent 
installations  when  properly  protected. 

The  relation  between  the  platinum-thermometer  scale 
and  the  gas-scale  is  fairly  well  established  up  to  1000°  C., 
which  is  near  the  limit  beyond  which  it  is  not  safe  to  use 
this  instrument  without  frequent  checking  of  its  calibra- 
tion. 

The  resistance  pyrometer  is  the  best  instrument  for 
differential  work  and  for  detecting  small  temperature 
changes  as  well  as  for  controlling  a  constant  temperature. 
Great  care  has  to  be  taken  that  the  platinum  does  not 
become  contaminated. 


CHAPTER  VI. 
THERMOELECTRIC   PYROMETER. 

Principle. — The  junction  of  two  metals  heated  to  a  given 
temperature  is  the  seat  of  an  electromotive  force  which  is 
a  function  of  the  temperature  only,  at  least  under  certain 
conditions  which  we  shall  define  further  on.  In  a  circuit 
including  several  different  junctions  at  different  tempera- 
tures the  total  electromotive  force  is  equal  to  their  alge- 
braic sum.  In  a  closed  circuit  there  is  produced  a  current 
equal  to  the  quotient  of  this  resultant  electromotive  force 
and  the  total  resistance. 

Experiments  of  Becquerel,  Pouillet,  and  Regnault. — 
It  was  Becquerel  who  first  had  the  idea  to  profit  from 
the  discovery  of  Seebeck  to  measure  high  temperatures 
(1830).  He  used  a  platinum-palladium  couple,  and  esti- 
mated the  temperature  of  the  flame  of  an  alcohol  lamp, 
finding  it  equal  to  135°.  In  reality  the  temperature  of  a 
wire  heated  in  a  flame  is  not  that  of  the  gases  in  combus- 
tion; it  is  inferior  to  this. 

The  method  was  studied  and  used  for  the  first  time  in 
a  systematic  manner  by  Pouillet;  he  employed  an  iron- 
platinum  couple  which  he  compared  with  the  air-ther- 
mometer previously  described  (page  66).  In  order  to 
protect  the  platinum  from  the  action  of  the  furnace-gases, 
he  enclosed  it  in  an  iron  gun-barrel  which  constituted  the 
second  metal  of  the  junction.  Pouillet  does  not  seem  to 
have  made  applications  of  this  method,  which  must  have 
given  him  very  discordant  results. 

120 


THERMOELECTRIC  PYROMETER.  121 

Edm.  Becquerel  resumed  the  study  of  his  father's 
couple  (platinum-palladium).  He  was  the  first  to  remark 
the  great  importance  of  using  in  these  measurements  a 
galvanometer  of  high  resistance.  It  is  the  electromotive 
force  which  is  a  function  of  the  temperature,  and  it  is  the 
current  strength  that  is  measured.  Ohm's  law  gives 

E=RL 

In  order  to  have  proportionality  between  these  quantities, 
it  is  necessary  that  the  resistance  of  the  circuit  be  invari- 
able. That  of  the  couple  necessarily  changes  when  it  is 
heated ;  this  change  must  be  then  negligible  in  comparison 
with  the  total  resistance  of  the  circuit. 

Edm.  Becquerel  studied  the  platinum-palladium  couple 
and  made  use  of  it  as  intermediary  in  all  his  measurements 
on  fusing-points,  but  he  did  not  use  it,  properly  speaking, 
as  a  pyrometer;  he  compared  it,  at  the  instant  of  observa- 
tion, with  an  air-thermometer  heated  to  a  temperature  near 
to  that  which  he  wished  to  measure.  He  also  tried  to 
make  a  complete  graduation  of  this  couple,  but  this  attempt 
was-  not  successful;  he  did  not  take  into  account  the 
irregularities  due  to  the  use  of  palladium;  besides,  he 
made  use  successively  for  this  graduation  of  a  mercury- 
thermometer  and  of  an  air-thermometer  which  did  not 
agree  with  each  other.  He  was  led  to  assume  for  the 
relation  between  the  temperature  and  the  electromotive 
force  a  very  complex  expression;  the  formulae  which  he 
gives  contain  together  twelve  parameters,  while  with  the 
parabolic  formula  of  Tait  and  Avenarius  two  suffice;  thus 

e=a+b(t-tQ)+c(t*-tQ'2), 

which  well  represents  the  phenomenon  for  the  couple  in 
question  up  to  1500°. 


122  HIGH   TEMPERATURES. 

Regnault  took  up  the  study  of  Pouillet's  couple,  and  he 
observed  such  irregularities  that  he  condemned  unre- 
servedly the  thermoelectric  method.  But  these  experi- 
ments are  hardly  conclusive,  for  he  does  not  seem  to 
have  considered  the  necessity  of  using  a  high-resistance 
galvanometer. 

Experiments  of  Le  Chatelier.  —  The  thermoelectric 
method  possesses  nevertheless  very  considerable  practical 
advantages  for  use  in  the  laboratory  as  well  as  industrially, 
such  as: 

Smallness  of  thermoelectric  substance; 

Rapidity  of  indications; 

Possibility  of  placing  at  any  distance  the  measuring 
apparatus. 

Also  Le  Chatelier  decided  to  take  up  the  study  of  this 
method,  intending  at  the  outset  not  to  make  disappear  the 
irregularities  which  seemed  inherent  to  the  phenomena  in 
question,  but  to  study  the  law  of  these  irregularities,  so 
as  to  determine  corrections  which  would  permit  of  mak- 
ing use  of  this  method,  at  least  industrially,  for  approxi- 
mate measurements.  These  investigations  showed  in 
their  turn  that  the  sources  of  error  observed  could  be  sup- 
pressed ;  the  principal  one,  and  the  only  serious  one,  came 
from  lack  of  homogeneity  of  the  metals  up  to  that  time 
employed. 

Iron,  nickel,  palladium,  and  their  alloys  are  absolutely 
unsuited  for  the  measurement  of  high  temperatures, 
because,  heated  in  certain  of  their  points,  they  give  birth 
to  parasite  currents,  sometimes  relatively  intense. 

Heterogeneity  of  Wires. — Here,  for  example,  are  the 
electromotive  forces  observed  in  carrying  a  Bunsen  flame 
along  beneath  a  wire  of  ferronickel  of  1  mm.  diameter  and 
50  cm.  long;  the  electromotive  forces  are  expressed  in 
microvolts  (millionths  of  a  volt): 


THERMOELECTRIC  PYROMETER.  123 

Distance...     0.05     0.10     0.15       0.20     0.30     0.35     0.40     0.50 
E.M.F.  .  ..    -200   +250   -150   -1000   -500    -200     -50   -200 

An  electromotive  force  of  1000  microvolts  is  that  given 
by  the  usual  couples  that  we  are  going  to  study  for  a  heat- 
ing of  100°.  With  such  anomalies  as  above  there  could 
hardly  be  any  measurements  possible. 

These  anomalies  may  sometimes  be  due  to  accidental 
variations  in  the  composition  of  the  wires,  but  in  general 
there  is  no  pre-existing  heterogeneity;  a  physical  hetero- 
geneity due  to  the  heating  is  produced.  Iron  and  nickel, 
heated  respectively  to  750°  and  380°,  undergo  an  allo- 
tropic  transformation,  incompletely  reversible  by  rapid 
cooling. 

In  the  case  of  palladium  there  are  produced,  besides, 
phenomena  of  hydrogenation  which  change  completely  the 
nature  of  the  metal,  so  that  a  metal  initially  homogeneous 
may  become  by  simple  heating  quite  heterogeneous  and 
form  a  couple. 

Certain  metals  and  alloys  are  quite  free  from  these 
faults,  notably  platinum  and  its  alloys  with  iridium  and 
rhodium.  The  irregularities  previously  observed  are  thus 
due  to  the  employment  of  iron  and  palladium  in  all  the 
couples  tried. 

A  second  source  of  error,  less  important,  comes  from  the 
annealing.  In  heating  a  wire  at  the  dividing-point  between 
the  hardened  part  and  the  annealed  part  there  is  developed 
a  current  whose  strength  varies  with  the  kind  of  wire  and 
the  degree  of  hardness.  The  twisting  that  a  wire  has 
undergone  at  a  point  suffices  to  produce  a  hardening. 
A  couple  whose  wires  are  hard  drawn  throughout  a  certain 
length  will  give  different  indications  according  to  the  point 
of  the  wire  where  the  heating  ceases.  Here  are  results  in 
microvolts  obtained  with  a  platinum  platinum-indium 


124  HIGH  TEMPEHATVHES. 


(20  per  cent  I2)   couple   (platinum-iridium  alloy  is  very 
easily  annealed): 

100°  445° 

Before  annealing  ....................   1100         7200 

After  annealing  .....................   1300         7800 

Difference  .....................     200          600 

We  shall  study  successively: 

1.  The  choice  of  the  couple; 

2.  The  choice  of  methods  of  measurements; 

3.  The  sources  of  error; 

4.  The  standardization. 

Choice  of  the  Couple.—  Account  must  be  taken  of  the 
electromotive  force,  the  absence  of  parasite  currents,  the 
inalterability  of  the  metals  used. 

a.  Electromotive  Force.  —  This  varies  enormously  from 
one  couple  to  another.  Below  are  several  such  electro- 
motive forces  given  between  0°  and  100°  by  metals  that 
can  be  drawn  into  wires  and  opposed  to  pure  platinum. 

Microvolts. 

Iron  ....................  ................  2100 

Hard  steel  ...............................  1800 

Silver  ...................................  900 

Cu  -f  10%  Al  .....  ........................  700 

Gold  ....................................  600 

Pt  +  10%Rh)  . 
Pt  +  10%lT    \  ........................... 

Cu  +  Ag  ......................  ...........  500 

Ferronickel  ..............................  100 

Nickel-steel  (5%  Ni)  ......................  0 

Manganese  steel  (13%  Mn)  .................  -   300 

Cu  +  20%  Ni  .............................  -  600 

Cu  +  Fe  +  Ni  .............................  -1200 

German  silver  (15%  Ni)  ...................  -1200 

"       (25%  Ni)  ...................  -2200 

Nickel  ...................................  -2200 

Nickel-steel  (35%  Ni)  .....................  -2700 

"      "      (75%  Ni)  .....  .  ...............  -3700 


THERMOELECTRIC  PYROMETER. 


125 


Barus*  studied  certain  alloys  between  0°  and  930°; 
he  obtained  the  following  results: 

Microvolts 

Indium  (2%) 791 

"       (5%) 2830 

"      (10%) 5700 

"      (15%) 7900 

"      (20%) 9300 

Palladium  (3%) 982 

(10%) 9300 

Nickel  (2%) 3744 

"     (5%) 7121 

Here  is  another  series  made  at  the  boiling-point  of 
sulphur  with  alloys  of  platinum  containing  2,  5,  and  10 
per  cent  of  another  metal: 


Metals. 

Au        Ag 

Pd 

Ir 

Cu 

2% 
5 
10 

2% 
5 
10 

2% 
5 
10 

-  242     -  18 
-  832     -105 
-1225     -158 

+  711 
+  869 
+  1127 

+  1384 
+  2035 

+3228 

+  410 
+392 

+  257 

Ni 

Co 

Fe 

Or 

Sn 

Zn 

+  2166 
+  3990 

+  5095 

+  26 
-170 
-  41 

+  3020 
+  3313 
+3962 

+  2239 
+  3123 
+3583 

+  261 
+  199 
+  151 

+396 
+  24 

Al 

Mn 

Mo 

Pb 

Sb 

Bi 

+  779 
+938 

+  758 
+  2206 

+  263 
+  1673 
+  766 

-268 
+  338 

+  1155 

+  245 

*  Barus,  at  the  same  time  as  Le  Chatelier,  studied  the  thermo- 
electric measurement  of  high  temperatures;  he  sought  to  determine 
the  temperatures  of  formation  of  the  rocks  of  the  earth's  crust  and 
also  to  determine  the  advantages  and  limitations  of  the  various 
pyrometric  methods;  his  very  considerable  investigations  are 
little  known.  There  is  a  great  mass  of  numerical  data  in  his  work, 
use  of  which  will  be  made  here. 


126 


HIGH  TEMPERATURES. 


Of  all  these  metals,  the  only  ones  to  keep  by  reason  of 
their  high  electromotive  force  are  the  alloys  of  platinum 
with  iron,  nickel,  chromium,  iridium,  and  rhodium.  The 
following  table  gives,  in  microvolts,  the  electromotive 
forces  of  the  10  per  cent  alloys  of  these  five  metals  up  to 
the  temperature  of  1500°: 


Temperatures. 

Fe 

Ni 

Cr 

Ir 

Rh. 

100° 
448 

930 

438 
3962 
9200 

646 
4095 
9100 

405 
3583 

517 
3228 
11000 

565 
3450 
8500 

1500 

19900 

20200 

15100 

6.  Absence  of  Parasite  Currents. — The  alloy  with  nickel 
gives  parasite  currents  of  great  intensity,  as  do  all  the  alloys 
of  this  metal-.  It  would  be  probably  the  same  with  iron, 
but  there  are  no  data  on  the  matter.  Chromium  does  not 
seem  to  present  the  same  inconvenience :  it  forms  an  alloy 
difficult  to  fuse  and,  for  this  reason,  difficult  to  prepare. 
With  the  alloys  of  iridium  and  of  rhodium  there  is  no  pro- 
duction of  parasite  currents. 

There  remain,  then,  but  three  metals  to  consider:  irid- 
ium, rhodium,  and  chromium.  Of  the  alloys  of  these 
metals  with  platinum,  that  of  iridium  is  the  one  which 
hardens  the  most  easily. 

c.  Chemical  Changes. — All  the  alloys  of  platinum  are 
slightly  alterable.  Those  of  nickel  and  of  iron,  at  high 
temperatures,  assume  a  slight  superficial  brownish  tint 
caused  by  oxidation  of  the  metal.  No  test  has  been  made 
to  see  if,  after  a  long  time,  this  attack  would  reach  even 
to  the  interior  of  the  wires. 

The  alloys  of  platinum,  and  platinum  itself,  become 
brittle  by  simply  heating  them  long  enough,  especially 


THERMOELECTRIC  PYROMETER.  127 

between  1000°  and  1200°;  this  is  due  without  doubt  to 
crystallization.  The  platinum-iridium  alloy  undergoes  this 
change  much  more  rapidly  than  the  platinum-rhodium, 
and  this  latter  more  rapidly  than  pure  platinum. 

But  a  much  more  grave  cause  of  the  alteration  of 
platinum  and  its  alloys  is  the  heating  to  high  temperatures 
in  a  reducing  atmosphere. 

All  the  volatile  metals  attack  platinum  very  rapidly,  and 
a  great  number  of  metals  are  volatile.  Copper,  zinc,  silver, 
antimony,  at  their  points  of  fusion,  already  emit  a  sufficient 
quantity  of  vapor  to  alter  rapidly  the  platinum  wires  placed 
in  the  neighborhood.  These  metallic  vapors,  that  of  silver 
excepted,  can  only  exist  in  a  reducing  atmosphere.  Among 
the  metalloids,  the  vapors  of  phosphorus  and  of  certain 
compounds  of  silicon  are  particularly  dangerous.  It  is  true 
that  one  is  rarely  concerned  with  these  uncombined  true 
metalloids,  but  their  oxides  in  the  presence  of  a  reducing 
atmosphere  are  more  or  less  completely  reduced.  In  the 
case  of  phosphorus  it  is  not  only  necessary  to  shun  phos- 
phoric acid,  but  also  acid  phosphates  of  all  the  metals  and 
the  basic  phosphates  of  the  reducible  oxides;  thus  silicon, 
silica  and  almost  all  the  silicates,  clay  included,  must  be 
avoided. 

The  reducing  flames  in  a  fire-clay  furnace  lead  little  by 
little  to  the  destruction  of  the  platinum  wires.  It  is  thus 
indispensable  to  protect  the  couples  against  any  reducing 
atmosphere  by  methods  which  will  be  indicated  further  on. 

In  taking  account  of  these  different  considerations, 
electromotive  force,  homogeneity,  hardness,  alterability 
by  fire,  we  are  led  to  give  the  preference  to  the  couple 
Pt-Pt  +  10%  Rh,  with  the  possibility  of  replacing  the 
rhodium  by  iridium  and  perhaps  by  chromium.  In  the 
case  of  iridium  it  is  necessary  to  recall  that  the  prelimi- 
nary annealing  of  the  wires  is  very  important,  and  that  pro- 


128  HIGH  TEMPERATURES. 

longed  heating  near  1100°,  even  in  an  oxidizing  atmos- 
phere, is  dangerous  for  the  couple. 

Methods  of  Electric  Measurements.—  Two  methods  may 
be  used  to  measure  the  electromotive  force  of  a  couple: 
the  method  of  opposition  and  the  galvanometric  method. 
From  the  scientific  point  of  view,  the  first  alone  is  rigorous  ; 
it  is  sometimes  made  use  of  in  laboratories.  "The  second 
method  is  simpler,  but  possesses  the  inconvenience  of 
giving  only  indirectly  the  measure  of  the  electromotive 
force  by  means  of  a  measurement  of  current  strength. 
This  inconvenience  is  more  apparent  than  real  hi  the 
later  forms  of  instrument,  as  will  be  shown. 

Method  of  Opposition.  —  A  complete  installation  consists 
of: 

1.  A  standard  cell,  which  should  not  have  any  current 
pass  through  it,  and  serves  to  determine,  as  term  of  com- 
parison, a  difference  of  potential  between  two  points  of  a 
circuit  through  which  there  is  a  current  given  by  an 
accumulator.  The  cell  used  may  be  a  Latimer-Clark, 
whose  electromotive  force  for  small  changes  in  tempera- 
ture is 

volts-0.00080(*°-15'). 


This  cell  is  made  up  as  follows:  zinc,  sulphate  of  zinc, 
mercurous  sulphate,  mercury.  The  zinc  sulphate  should 
be  perfectly  neutral  ;  for  that  the  saturated  solution  of  the 
salt  is  heated  to  40°  or  more  with  an  excess  of  zinc  oxide 
to  saturate  the  free  acid,  is  then  treated  with  mercurous 
sulphate  to  remove  the  excess  of  zinc  oxide  dissolved  in 
the  sulphate,  and  finally  crystallization  is  produced  at  0°; 
one  thus  obtains  crystals  of  zinc  sulphate  which  can  be 
immediately  used. 

This  element  is  very  constant.  With  a  surface  of  zinc 
electrode  equal  to  100  sq.  cm.  and  a  resistance  of  1000 


THERMOELECTRIC  PYROMETER.      129 

ohms,  the  dropping  off  of  the  electromotive  force  of  the 
cell  in  action  does  not  reach  ToVo ;  with  100  ohms  only, 
this  would  be  -%$-$.  Practically  it  is  possible,  with  a  resist- 
ance of  1000  ohms,  to  limit  the  surface  of  the  electrodes 
to  30  sq.  cm.,  and  to  do  away  with  the  use  of  accumulators. 
But  then  the  theoretical  advantage  of  the  absolute  rigor 
of  the  method  employed  is  lost. 

There  are  other  forms  of  standard  cell  which  possess 
the  advantages  of  portability  and  small  temperature  coeffi- 
cient rendering  them  better  adapted  for  ordinary  use  than 
the  original  Clark  form.  The  Carhart-Clark  cell  is  made 
with  unsaturated  mercurous  sulphate  and  has  the  E.M.F. 

6=1.440-0.00056(^-15°). 

In  the  Weston  cadmium  cell,  cadmium  and  cadmium- 
sulphate  replac.e  the  zinc  and  zinc-sulphate  of  the  Clark 
cell,  and  in  the  portable  form  of  the  cell  the  cadmium- 
sulphate  is  unsaturated.  This  cell  has  no  temperature 
coefficient  so  that  no  precautions  as  to  temperature  control 
have  to  be  taken.  This  cell  also  recovers  rapidly  after 
maltreatment.  Its  E.M.F.  is  1.0198  volts. 

The  values  of  the  E.M.F.s  given  above  are  in  inter- 
national volts  which  are  legal  in  the  United  States  and 
used  by  the  National  Bureau  of  Standards.  The  Reichs- 
anstalt  have  found  the  E.M.F.  of  the  Clark  cell  to  be 
1.433,  and  use  this  value. 

2.  A  resistance-box  which  includes  a  fixed  resistance  of 
about  1000  ohms  and  a  series  of  resistances  of  0  to  10 
ohms,  permitting  by  their- combinations  to  realize  in  this 
interval  'resistances  varying  by  tenths  of  an  ohm.  One 
may,  for  greater  simplicity,  but  by  sacrificing  precision, 
replace  this  series  of  small  resistances  by  a  single  Pouillet's 
rheostat  having  a  total  resistance  of  10  ohms.  This  appa- 


130  HIGH   TEMPERATURES. 

ratus  consists  of  two  parallel  wires  of  a  meter  in  length 
and  3  mm.  in  diameter,  made  of  an  alloy  of  platinum  and 
3%  copper. 

3.  A  sensitive  galvanometer  giving  an  appreciable  deflec- 
tion for  10  microvolts.  It  is  placed  in  the  circuit  of  the 
couple.  Use  may  be  made  here  of  a  galvanometer  Deprez- 
d'  Arson  val  of  small  resistance,  since  this  is  a  case  of  reduc- 
tion to  zero. 

Principle  of  the  Method.  —  In  order  to  make  an  experi- 
ment, one  places  by  trial  the  two  extremities  of  the  couple 
in  contact  with  two  points  of  the  circuit  of  the  cell  chosen 
so  that  the  couple  is  not  traversed  by  any  current. 

In  these  conditions  the  electromotive  force  of  the  couple 
is  equal  and  of  opposite  sign  to  the  difference  of  potential 
between  the  two  points  of  the  circuit,  and  this,  in  calling 

JZ  the  electromotive  force  of  the  cell, 

R  the  total  resistance  of  the  circuit, 

r  the  resistance  between  the  two  points  considered, 
has  for  value 


A  modification  of  this  method  eliminating  the  standard 
cell  in  actual  wotk  with  the  couple  has  its  advantages.  A 
storage  cell  at  W  (Fig.  24)  is  in  series  with  a  rheostat  R  and 
a  series  of  coils  or  combinations  of  coils  and  bridge  wire 
represented  by  AB.  The  E.M.F.  of  the  standard  cell 
at  E  is  balanced  against  that  of  the  battery  W  by  varying 
R,  the  points  of  contact  ifa  and  Mf  being  at  A  and  B 
and  the  balance  indicated  by  no  current  in  the  galvanom- 
eter. The  standard  cell  is  no^  replaced  at  E  by  the 
couple  whose  E.M.F.  is  to  be  measured;  M  and  Mf  are 
then  varied  in  position  until  a  balance  is  again  obtained; 
then 


THERMOELECTRIC  PYROMETER. 
MM' 


131 


e=E. 


AB  ' 


This  is  the  simplest  form  of  potentiometer. 

Use  of  a  Potentiometer. — For  exact  measurements  the 
resistance-box,  mentioned  above,  may  be  replaced  to 
great  advantage  by  some  form  of  potentiometer,  of  which 


FIG.  24. 

there  are  several  on  the  market,  suitable  for  the  deter- 
mination of  small  electromotive  forces  and  whose  prin- 
ciples we  have  just  described.  This  type  of  instrument  is 
illustrated  in  Fig.  23,  p.  117,  and  has  the  great  convenience  of 
being  direct  reading,  giving  the  electromotive  force  directly 
in  decimals  of  a  volt,  so  that  the  E.M.F.  of  a  couple  at 
any  temperature  is  determined  in  a  few  seconds  to  an 
accuracy  of  one  microvolt  with  a  sensitive  galvanometer. 
The  method  of  taking  a  measurement  is  as  follows: 
The  dials  being  set  in  any  position  whatever,  the  standard 
cell,  which  is  in  series  with  all  the  coils  in  the  box,  is 
balanced  against  the  battery  by  varying  the  rheostat; 
the  switch  is  then  thrown  to  the  E.M.F.  side  which  throws 
out  the  standard  cell,  and  the  E.M.F.  of  the  couple,  at- 
tached through  leads  and  a  reversing  switch  to  the  binding 


132  HIGH  TEMPERATURES. 

posts  marked  E.M.F.,  is  measured  by  turning  the  dials 
until  a  balance  is  reached. 

For  thermoelectric  work  it  is  not  necessary  to  have  an 
extremely  high  resistance  potentiometer,  1000  ohms  suf- 
ficing, but  the  lower  this  resistance  the  greater  the  care 
required  in  the  construction  and  use  to  avoid  uncertain 
electrical  contacts.  In  practice  also  the  direction  of  the 
E.M.F.s  should  be  reversed  for  every  reading  to  eliminate 
thermo-E.M.F.s.  A  sensitive  galvanometer  is  necessary 
for  precise  work. 

Compensation  Method, — This  is  a  modification  of  the 
preceding  eliminating  the  use  of  a  potentiometer  or  care- 
fully calibrated  resistance-box,  but  requiring  a  calibrated 
milliammeter  and  one  or  more  well-known  resistances. 
This  method  was  first  used  by  Holman  in  thermoelectric 
work,  and  Fig.  25  illustrates  the  principle.  M  is  a  milliam- 


FIG.  25. 


meter  and  r  a  small  (O.lw)  known  resistance,  R  a  rheostat 
with  fine  adjustment;  G  the  galvanometer,  and  T  the  thermo- 


THERMOELECTRIC  PYROMETER.  133 

couple.  The  deflection  of  G  is  brought  to  zero  by  varying 
R  when  the  product  of  the  current  given  by  M  and  the  re- 
sistance r  gives  the  desired  E.M.F.  With  a  series  of  coils 
to  substitute  at  r,  the  range  of  measurable  temperature  may 
be  indefinitely  extended. 

Siemens  and  Halske  sell  a  convenient  form  of  this  appa- 
ratus as  devised  by  Lindeck  of  the  Reichsanstalt. 

Various  other  special  forms  of  apparatus  for  the  exact 
measurement  of  thermocouple  E.M.F.s  have  been  devised, 
but  they  are  all  modifications,  more  or  less  complicated, 
of  the  above. 

Gcdvanometric  Method.  —  The  measurement  of  an  elec- 
tromotive force  may  be  reduced  to  that  of  a  current;  it 
suffices  for  that  to  put  the  couple  in  a  circuit  of  known 
resistance,  and  from  Ohm's  law  we  have 


R' 


If  the  resistance  is  not  known,  but  is  constant,  the 
electromotive  force  will  be  proportional  to  the  current 
strength,  and  that  will  suffice,  on  the  condition  that  the 
graduation  of  the  couple  is  made  with  the  same  resistance. 
If  this  resistance  is  only  approximately  constant,  the  rela- 
tion of  proportionality  will  be  only  approximately  exact. 

This  method  is  the  one  used  in  practically  all  industrial 
practice,  and  to-day  galvanometers  can  be  had  satisfying 
all  the  requirements  of  which  we  shall  treat  in  the  follow- 
ing paragraphs.  In  many  quarters  the  thermoelectric 
pyrometer  has  been  discredited  because  instruments  giving 
evidently  unreliable  results  were  used.  With  a  better 
understanding  of  the  requirements  and  the  meeting  of 
them  by  manufacturers  this  prejudice  is  disappearing. 

Resistance  of  Couples.  —  The  wires  of  the  couple  make 


134 


HIGH   TEMPERATURES. 


necessarily  a  part  of  the  circuit  in  which  the  current 
strength  is  measured,  and  their  resistance  varies  with 
increase  of  temperature.  It  is  important  to  take  account 
of  the  order  of  magnitude  of  this  inevitable  change  of 
resistance. 

Barus  has  made  a  systematic  series  of  observations  on 
the  alloys  of  platinum  with  10  per  cent  of  other  metal. 
The  relation  between  the  resistance  and  the  temperature 
being  of  the  form 

Rt  =  R0(l+at), 
he  obtained  the  following  results: 


Pt 

(pure) 

Au 

Ag 

Pd 

Ir 

24.4 
1.2 

Cu 

Ni 

Fe 

Cr 

Sn 

Specific    resist- 
ance   in   mi- 
crohms (/?).  . 
lOOOa 

15.3 
2.2 

25.6 

1 

34.8 
0.7 

23.9 
1.2 

63.9 
0.2 

33.7 
0.9 

64.6 
0.4 

42 
0.5 

39 

0.7 

Other  tests  gave  the  figures  below: 


5% 
Al 

5% 
Mn 

10% 

Mo 

5% 
Pb 

2% 
Sb 

5% 
Bi 

2% 
Zn 

5% 
Zn 

R0 

22 

50 

17.6 

7  7 

29.5 

16  6 

47.8 

25 

lOOOa  

1.5 

0  4 

1.9 

1   8 

1 

2 

0.3 

1.1 

The  coefficient  a  is  taken  between  0°  and  357°  (boiling- 
point  of  mercury). 

The  experiments  of  Le  Chatelier,  for  the  couples  that 
he  used,  gave  the  following  results: 

For  platinum 

R=  11.2(1+0.0020  between  0°  and  1000°, 


THERMOELECTRIC  PYROMETER.  135 

For  rhodium-platinum  (10%  Rh) 

12=27(1+0.00130  between  0°  and  1000°. 

Holborn  and  Wien  found  for  pure  platinum 

#=7.9(1+0.00310  between  0°  and  100°, 
#=7.9(1+0.00280  between  0°  and  1000°. 

In  the  greater  number  of  cases  use  is  made  of  couples 
1  m.  in  length,  whose  wires  are  0.5  mm.  in  diameter;  their 
resistance,  which  is  about  2  ohms  cold,  is  doubled  at  1000°. 
If  use  is  made  then  of  a  galvanometer  of  a  resistance  of 
200  ohms  and  if  the  variation  of  the  resistance  of  the 
couple  is  neglected,  the  error  is  equal  to  T^.  In  general 
this  error  is  still  less  except  in  certain  industrial  uses. 
Thus  in  the  laboratory  the  length  heated  rarely  exceeds 
10  cm.,  and  then  the  error  reduces  to  T  l  . 

Galvanometers.  —  The  earliest  measurements,  those  of 
Becquerel  and  of  Pouillet,  were  made  with  needle-galvanom- 
eters controlled  by  terrestrial  magnet  ism.  These  appara- 
tus, sensible  to  jarring,  require  delicate  adjustment,  and 
the  readings  take  a  long  time.  The  use  of  these  instru- 
ments would  have  prevented  the  method  from  becoming 
practical.  It  is  only  thanks  to  the  use  of  movable-coil 
galvanometers  of  the  Deprez-d'  Arsonval  type  that  the  ther- 
mo  electric  pyrometer  has  been  able  to  become,  as  it  is 
to-day,  an  apparatus  in  current  usage. 

This  apparatus  (Fig.  26)  is  composed  of  a  large  horse- 
shoe magnet  between  whose  poles  is  suspended  a  movable 
frame  through  which  the. current  passes.  The  metallic 
wires,  which  serve  at  the  same  time  to  suspend  the  coil  and 
bring  in  the  current,  undergo  then  a  torsion  which  is 
opposed  to  the  displacement  of  the  coil. 

The  latter  stops  in  a  position  of  equilibrium  which 


136  HIGH  TEMPERATURES. 

depends  both  on  the  strength  of  the  current  and  the  value  of 
the  torsion  couple  of  the  wires. 
To  these  two  forces  is  added,  in 
general,  a  third,  due  to  the  weight 
of  the  coil,  which  causes  disturbing 
effects  often  very  troublesome. 
We  shall  speak  of  this  further  on. 
The  measurement  of  the  angular 
displacement  of  the  coil  is  made 
sometimes  by  means  of  a  pointer 
which  swings  over  a  divided  scale, 
more  often  by  means  of  a  mirror 
which  reflects  on  a  semitrans- 
FIG.  26.  parent  scale  the  image  of  a  wire 

stretched  before  a  small  opening  conveniently  lighted. 

These  movable-coil  galvanometers  were  for  a  long  time 
considered  by  physicists  as  unsuited  for  any  quantitative 
measurements;  they  were  only  employed  in  null  methods 
and  made  accordingly.  In  order  to  render  them  suitable 
for  quantitative  measurements  of  current  it  was  necessary 
to  attend  to  a  series  of  details  of  construction,  previously 
neglected.  Here  are  the  most  important  among  these. 

1.  The  movable  coil  should  possess  a  resistance  as  little 
variable  as  possible  with  the  surrounding  temperature  in 
order  to  avoid  corrections  always  very  uncertain.     The 
coils  of  copper  wire  ordinarily  used  to  augment  the  sensi- 
bility should  be  absolutely  discarded;  use  should  be  made 
of  coils  of  German  silver  or  of  similar  metal  with  small 
temperature  coefficient  such  as  manganin. 

2.  The  spaces  which  separate  the  coils,  from  the  poles 
of  the  magnet,  on  the  one  hand,  and  from  the  central 
soft-iron  core  on  the  other,  should  be  sufficiently  great  to 
avoid  with  certainty  any  accidental  friction  which  would 
prevent  the  free  movement  of  the   coil.      A  width  of 


THERMOELECTRIC  PYROMETER.  137 

2  mm.  is  convenient;  it  will  hardly  do  to  decrease  this. 
The  rubbings  to  look  out  for  do  not  come  from  the  direct 
contact  of  the  frame  with  the  magnet :  these  latter  are  too 
visible  to  escape  unseen.  Those  which  are  to  be  guarded 
against  come  from  the  rubbing  of  filaments  of  silk  which 
stand  out  from  insulating  covering  of  the  metallic  wires, 
and  from  the  ferruginous  dust  which  clings  to  the  magnet. 
It  is  here,  it  would  seem,  that  the  most  serious  source  of 
error  is  met  with  in  the  use  of  the  movable-coil  galvanom- 
eter as  measuring  instrument.  There  is  no  warning  indi- 
cation of  these  slight  rubbings  which  limit  the  displacement 
of  the  coil  without,  however,  taking  from  it  its  apparent 
mobility. 

3.  The  suspending  wire  should  be  as  strong  as  may  be 
to  support  the  coil  without  being  exposed  to  breaking  by 
shocks ;  on  the  other  hand,  it  should  be  very  fine,  so  as  not 
to  have  too  great  a  torsion  couple.  Two  different  artifices 
help  to  reconcile  somewhat  these  two  opposed  conditions: 
the  use  of  the  mode  of  suspension  of  Ayrton  and  Perry, 
which  consists  in  replacing  the  straight  wire  by  a  spiral 
made  of  a  flattened  wire,  or  more  simply  the  use  of  a 
straight  wire  flattened  by  a  passage  between  rollers. 

The  first  method  offers  the  greatest  security  from 
shocks;  it  is,  on  the  other  hand,  more  difficultly  realizable; 
minute  precautions  should  be  taken  to  prevent  any  rubbing 
between  adjoining  spirals.  The  second  method  allows 
more  easily  having  the  large  angular  displacements  which 
are  indispensable  when  it  is  desired  to  take  readings  upon 
a  dial. 

The  most  essential  property  necessary  for  the  wires  is 
absence  of  .permanent  torsion  during  the  operations. 
These  torsions  cause  changes  of  zero  which  may  render 
worthless  all  the  observations  if  account  is  not  taken  of 
this,  which  complicates  matters  considerably  if  such  cor- 


138  HIGH   TEMPERATURES. 

rection  has  to  be  made.  This  result  is  reached  by  using 
wires  as  long  as  possible,  having  not  less  than  100  mm. 
length,  and  by  avoiding  giving  to  them  an  initial  torsion, 
a  precaution  that  should  be  kept  constantly  in  mind,  which 
it  often  is  not.  When  one  wishes  to  adjust  the  coil  to  the 
zero  of  graduation,  one  turns  often  haphazard  either  one  of 
the  wires ;  it  may  be  then  that  each  of  the  wires  is  given 
an  initial  torsion  of  considerable  magnitude  and  of  oppo- 
site sign.  If  the  two  wires  are  not  symmetrical,  as  is 
ordinarily  the  case,  the  permanent  deformation  resulting 
from  this  exaggerated  torsion  will  cause  a  continual  dis- 
placement of  the  zero  which  may  last  for  weeks  and 
months,  increasing  or  decreasing  during  the  observations 
according  to  the  direction  of  displacement  of  the  coil.  This 
torsion  is  easy  to  obviate  at  the  time  of  construction,  but 
it  is  not  possible  to  verify  later  its  absence  in  the  case  of 
round  wires  or  spirals  except  by  dismounting  the  appa- 
ratus. On  the  contrary,  by  the  use  of  stretched  flat  wires 
it  is  very  easy  upon  simple  examination  to  determine  the 
existence  or  absence  of  torsion.  This  is  another  reason 
for  employing  them. 

Finally,  use  must  be  made  of  wires  having  a  very  high 
elastic  limit.  For  that  it  is  necessary  that  the  metal  has 
been  hardened,  and  besides  that  the  metal  does  not  undergo 
spontaneous  hardening  at  ordinary  temperatures.  Silver, 
generally  employed  as  suspension  wire,  is  worthless.  A 
metal,  as  iron,  which  even  after  annealing  possesses  a  high 
elastic  limit,  would  be  perfect  if  it  were  not  for  its  too 
great  alterability.  One  cannot  be  sure  of  having  uniform 
hardening,  because  the  soldering  of  wires,  indispensable 
to  assure  good  contacts,  anneals  them  throughout  a  certain 
length.  German  silver  is  the  metal  the  most  frequently 
used  in  galvanometer  suspensions  destined  for  pyro- 
metric  measurements.  The  alloy  of  platinum  with  10  per 


THERMOELECTRIC  PYROMETER.  139 

cent  of  nickel  seems  preferable;  after  annealing  it  has  a 
high  elastic  limit,  and  possesses  a  tenacity  much  higher 
than  that  of  German  silver.  Its  disadvantage  is  to  possess 
a  limit  of  elasticity  twice  as  great,  which  reduces  by  one- 
half  the  deflections  of  a  given  cross-section  of  wire.  Phos- 
phor-bronze also  gives  good  results. 

4.  Installation  of  the  apparatus  for  the  galvanometers, 
in  which  the  coil  is  carried  by  two  opposed  stretched  wires, 
necessitates  special  precautions. 

In  the  first  place  it  should  be  located  beyond  the  influ- 
ence of  j  airings  of  the  ground,  which  render  reading 
impossible;  then  it  is  necessary  that  its  position  remain 
rigorously  fixed.  If,  in  fact,  the  two  extreme  points  of 
suspension  of  the  wires  are  not  exactly  hi  the  same  vertical, 
and  if  the  centre  of  gravity  of  the  coil  is  not  exactly  in  the 
line  of  the  two  points  of  suspension,  two  conditions  which 
can  be  never  rigorously  realized,  the  apparatus  constitutes 
a  bifilar  pendulum  of  great  sensibility.  The  slightest 
jarring  suffices  to  provoke  very  considerable  angular  dis- 
placements of  the  coil.  To  avoid  them,  the  apparatus 
should  rest  upon  a  metallic  support  attached  to  a  wall  of 
masonry.  When  the  apparatus  is  placed,  as  is  often  the 
case,  upon  a  wooden  table  resting  upon  an  ordinary  wooden 
floor,  in  order  to  obtain  a  deflection  of  the  coil,  and  in 
consequence  a  displacement  of  the  zero,  it  suffices  to  walk 
around  the  table,  which  causes  the  floor  to  bend  slightly, 
or  to  provoke  a  current  of  air,  which,  in  changing  the 
hygrometric  state  of  the  legs  of  the  table,  causes  it  to  tip 
somewhat. 

Coils  freely  suspended  from  above  have  not  these  dis- 
advantages. 

Different  Types  of  Galvanometer. — A  series  of  galvanom- 
eters have  been  studied  especially  in  view  of  pyrometric 
measurements;  we  shall  pass  them  rapidly  in  review. 


140  HIGH  TEMPERATURES. 

For  laboratory  researches  the  usual  swinging-coil  galva- 
nometer as  made  by  Carpentier  is  often  used.  One  must 
make  sure  that  these  instruments  satisfy  well  the  indis- 
pensable conditions  which  we  have  mentioned,  which  is 
not  always  the  case  when  these  instruments  have  been  con- 
structed with  reference  to  the  ordinary  experiments  of 
physics.  These  conditions  are: 

Coil  of  German-silver  or  low-temperature-coefficient 
wire  of  a  resistance  of  at  least  200  ohms;  400  ohms  is 
better. 

Sufficient  free  space  between  coil  and  magnet. 

Invariability  of  zero,  even  after  a  considerable  deflection 
of  coil. 

Installation  on  a  firm  support  and  levelling  device. 

This  laboratory  apparatus,  the  only  one  which  existed 
At  the  time  of  the  first  investigations  of  Le  Chatelier,  was 
not  transportable,  and  could  not  be  arranged  for  experi- 
ments in  industrial  works.  It  was  then  necessary  to 
devise  a  special  model  of  galvanometer  easy  to  carry 
about  and  to  put  in  place.  The  apparatus  (Fig.  27)  is 
composed  of  two  parts,  the  galvanometer  and  the  trans- 
parent scale  with  its  light.  The  two  parts  are  symmetrical 
and,  for  transportation,  may  be  fixed  back  to  back  on  the 
same  plank  carrying  a  handle.  For  observations  they. are 
fastened  to  a  wall  by  means  of  two  nails  driven  in  at  a 
suitable  distance  apart.  The  suspension  wires,  in  case  of 
breakage,  may  be  immediately  replaced.  They  carry, 
soldered  to  their  two  ends,  small  nickel  spheres,  which  one 
has  only  to  slip  on  to  forked  pieces  attached  to  the  top  and 
bottom  of  the  coil,  and  to  the  supports  of  the  apparatus, 
respectively.  The  mirror  consists  of  a  plano-convex  lens, 
silvered  on  the  plane  face,  which  gives  much  sharper  and 
brighter  images  than  the  ordinary  small  mirrors  with 
parallel  faces. 


THERMOELECTRIC  PYROMETER. 


141 


Lately,  Carpentier  has  made  for  the  same  purpose  a 
galvanometer  in  which  the  readings  are  taken  by  means  of 
a  microscope.  It  is  an  easily  transportable  apparatus  and 
very  convenient.  It  has  only  the  fault  to  be  subject  to  a 
displacement  of  the  zero  resulting  from  the  unsymmetrical 
heating  of  the  body  of  the  microscope  by  the  small  lamp 


FIG.  '27. 

which  lights  the  reticule.  The  stretched  wires  are  replaced 
by  large  spirals  which  offer  an  absolute  resistance  to  rup- 
ture by  shock  during  transportation. 

The  use  of  this  apparatus  necessitates  an  arrangement 
which  permits,  during  the  observations,  putting  the  gal- 
vanometer on  open  circuit  so  as  to  verify  the  zero  reading. 

In  the  three  preceding  galvanometers  the  measurement 
of  the  deflection  of  the  coil  is  made  by  optical  means;  in 
the  three  following,  the  measurement  is  made  by  means  of 
a  needle  swinging  over  a  scale. 

After  a  study  made  by  Holborn  and  Wien  at  the 
Physikalische  Reichsanstalt  in  Berlin  of  the  Le  Chatelier 


142 


HIGH  TEMPERATURES. 


thermoelectric  pyrometer,  the  firm  of  Kayser  and  Schmidt 
devised  a  needle-galvanometer  (Fig.  28)  which  works 
fairly  well,  although  the  early  forms  of  this  instrument 
were  of  too  low  resistance  for  many  industrial  purposes. 
It  has  the  disadvantage  of  being  somewhat  fragile.  The 
suspending  wire  of  the  coil  does  not  seem  to  have  more 
than  1/20  mm.  diameter ;  the  mounting  of  the  apparatus  is 
quite  complicated.  Repairs  cannot  readily  be  made 
either  in  the  laboratory  or  works. 


FIG.  28. 

The  firm  Siemens  and  Halske,  which  has  commenced 
recently  to  build  Deprez-d'Arsonval  galvanometers,  has 
also  devised  a  model  of  needle-galvanometer  suitable  for 
temperature  measurements  (Fig.  29).  Its  resistance  is 
340  ohms,  or  400  ohms  in  the  later  forms;  the  scale  has 
180  divisions,  each  corresponding  to  10  microvolts.  There 
is  also  a  second  graduation  which  gives  the  temperature 
directly  with  the  couple  sold  with  the  apparatus.  Com- 
mutators allow  of  putting  the  apparatus  successively  in 
communication  with  different  thermoelectric  couples,  if 
it  is  desired  to  take  simultaneously  several  sets  of  obser- 
vations. 


THERMOELECTRIC  PYROMETER. 


143 


FIG.  29. 


FIG.  30. 


144  HIGH  TEMPERATURES. 

Pellin,  of  Paris,  has  made,  from  designs  of  Le  Chatelier, 
a  needle-galvanometer  (Fig.  30)  of  simple  construction 
which  can  be  repaired  where  it  stands.  The  very  long 
suspension  wire  is  of  10  per  cent  nickel-platinum;  it  has 
V10  mm.  diameter  and  is  drawn  out  flat. 

The  lower  wire  is  made  of  a  spiral  of  the  same  wire  of 
YJJO  mm.  diameter,  which  is  situated  in  the  interior  of  the 
iron  core  so  as  to  insure  uniformity  of  temperature. 
When  the  spirals  of  the  suspension  are  unequally  heated 
by  radiation  from  the  room  or  for  other  reason,  there 
results  considerable  displacement  of  the  zero.  A  spirit- 
level  permits  of  rendering  the  apparatus  vertical,  but  it  is 
prudent,  by  reason  of  the  length  of  the  suspension  wire,  to 
make  sure  directly  of  the  absence  of  nibbing  on  the  coil. 
For  this  a  slight  jar  is  given  to  the  apparatus;  the  point 
of  the  needle  should  take  up  and  keep  for  a  long  time  a 
slow  oscillatory  movement  in  the  direction  of  its  length; 
the  transverse  oscillations  ceasing  rapidly  indicate  friction 
upon  the  coil.  Evidently  use  may  be  made  of  a 'great 
number  of  other  models  of  galvanometer  which  are  to  be 
found  on  the  market;  but  it  is  necessary  to  make  sure 
in  the  first  place  that  they  satisfy  the  conditions  necessary 
for  good  temperature  measurement,  which  is  rarely  the 
case. 

Requirements  of  Industrial  Practice. — In  many  indus- 
trial operations  it  is  desirable  to  know  a  temperature  in 
the  range  400°  C.  to  1500°  C.  to  10  degrees.  This  accu- 
racy can  be  obtained  with  industrial  forms  of  the  thermo- 
electric pyrometer,  but  only  when  certain  conditions  are 
fulfilled  by  the  maker  and  by  the  user. 

The  instrument,  sufficiently  sensitive  and  at  the  same 
time  robust,  should  have  an  open  scale  carefully  cali- 
brated; the  resistance  of  the  galvanometer  should  be 
400  ohms  at  least,  for  use  with  ordinary  platinum-metal 


THERMOELECTRIC  PYROMETER.  145 

thermocouples,  so  that  varying  depths  cf  immersion 
and  changes  of  resistance  of  the  couple  wires  with  tem- 
perature will  not  appreciably  affect  the  galvanometer 
readings;  the  temperature  coefficient  of  the  instrument 
should  be  negligible  and  there  should  be  no  secondary 
thermal  sources  of  electromotive  force  present;  the 
constancy  of  the  zero  should  be  within  the  desired  limit 
of  precision  even  with  continued  deflections  at  the  higher 
points  of  the  scale;  a  levelling  device  should  be  provided 
and  the  effect  of  non-levelling  on  the  readings  of  the 
instrument  should  be  small.  This  last  is  perhaps  the 
hardest  requirement  to  fulfil,  and  it  is  necessary  for  the 
user  to  carefully  level  any  industrial  instrument  and 
verify  its  zero  reading  before  any  measurements  are  taken. 
If  the  wires  of  the  couple  are  attached  directly  to  the  gal- 
vanometer, as  is  usually  the  case,  care  must  be  taken  that 
the  temperature  of  the  binding-posts  remains  constant, 
for  if  they  are  heated  or  cooled  they  also  become  sources 
of  E.M.F.  and  so  change  the  readings  of  the  galvanometer, 
and  in  general  if  anywhere  in  the  circuit  there  are  dissimilar 
metals  joined  together  there  will  be  parasite  currents 
developed  at  these  junctions  for  changes  of  temperature. 
The  user  should  know  at  what  temperature  the  scale 
of  his  instrument  is  correct  and  should  be  enabled  to 
correct  for  changes  in  temperature  of  the  ''cold"  junc- 
tions. 

If,  for  example,  the  scale  of  the  galvanometer  is  correct 
when  the  cold  junctions  are  at  0°  C.,  the  indicated  tem- 
perature given  by  the  galvanometer  should  be  increased 

t° 

by  — ,where  t°\s  the  actual  temperature  of  the  cold  junctions, 
t-  .  « 
t°  being  less  than  30°  C. 

If  a  new  couple  is  substituted,  the  E.M.F.  scale  of  the 
galvanometer  will  still  be  correct,  but  unless  the  new 


146  HIGH  TEMPERATURES. 

couple  is  identical  with  the  old,  the  temperature  scale  will 
no  longer  hold. 

Arrangement  of  the  Wires  of  the  Couple. — For  good 
working  of  the  couple  there  are  certain  practical  precau- 
tions to  be  taken,  which  we  shall  consider. 

Junction  of  the  Wires. — The  contacts  of  the  different 
parts  of  the  circuit  should  be  assured  in  a  positive  manner; 
the  best  way  is  to  solder  them.  Binding-screws  often 
work  loose  in  time,  or  the  metallic  surfaces  in  contact 
become  oxidized.  The  importance  of  this  precaution 
varies  with  the  conditions  of  the  experiments;  one  can 
dispense  with  it  for  experiments  that  last  only  a  few  hours, 
because  there  is  little  chance  that  the  contacts  become 
modified  in  so  short  a  time;  soldering  is  on  the  contrary 
indispensable  in  an  industrial  installation  which  will  have 
to  be  used  for  months  without  being  tested  anew. 

But  in  any  case  the  soldering  together  of  the  two  leads 
of  the  couple  is  absolutely  indispensable.  It  is  quite  true 
that  the  electromotive  force  is  independent  of  the  manner 
of  making  contact.  The  two  wires  twisted  together  or 
soldered  will  give  at  the  same  temperature  the  same  elec- 
tromotive force.  But  under  the  action  of  heat  the  twisted 
parts  are  soon  loosened,  and  there  result  bad  contacts 
which  increase  the  resistance  of  the  whole  circuit.  In 
general  this  accident  is  not  noticed  until  the  untying 
is  almost  complete,  so  that  one  may  make  before  this 
a  whole  series  of  false  measurements  without  being 
warned. 

The  best  method  of  soldering  is  the  autogene  junction 
by  direct  fusion  of  the  wires  of  the  couple;  it  is  necessary, 
in  order  to  effect  this,  to  have  oxygen  at  hand.  One  com- 
mences by  twisting  the  two  leads  together  for  a  length  of 
about  5  mm.,  and  they  are  then  clamped  above  an  oxy- 
hydrogen  blast-lamp.  Oxygen  is  admitted  through  the 


THERMOELECTRIC  PYROMETER.  147 

central  tube,  and  gas  through  the  annular  space;  the 
oxygen  is  allowed  to  flow  in  normal  quantity,  and  the 
gas  in  feeble  quantity,  then  one  opens  progressively  the 
gas-cock.  At  a  certain  instant  one  sees  the  extremities  of 
the  wires  melt,  giving  off  sparks;  the  gas  is  then  shut  off. 
If  one  waits  too  long,  the  junction  will  melt  completely 
and  the  two  wires  separate.  With  a  little  practice  a 
junction  can  be  made  by  touching  together,  hi  the  oxyhy- 
drogen  blast,  the  two  wires  held  in  the  hand. 

In  default  of  oxygen,  the  wires  may  be  soldered  with 
palladium,  which  can  be  melted  by  means  of  a  blast-lamp 
furnished  with  air,  taking  care  to  reduce  the  action  of 
radiation.  A  hole  is  cut  in  a  piece  of  charcoal  in  which 
is  placed  the  junction  of  the  two  wires  twisted  together 
after  having  wound  about  it  a  wire  or  a  small  strip  of 
palladium,  and  the  flame  of  the  lamp  is  then  directed  upon 
the  junction. 

In  the  cases  in  which  the  couple  is  not  to  be  used  above 
1000°,  and  only  in  these  cases,  the  soldering  may  be  done 
still  more  simply  by  the  use  of  gold;  the  ordinary  Bunsen 
flame  is  sufficient  to  make  this  junction. 

Insulation  and  Protection  of  the  Couple. — The  two  leads 
should  be-  insulated  from  one  another  throughout  their 
length.  For  this,  use  is  made  in  the  laboratory  of  glass 
tubes  or  pipe-stems,  or  better  still  of  an  asbestos  thread 
wound  about  the  two  wires,  by  crossing  it  each  time 
between  the  two  (Fig.  35)  so  as  to  make  a  double  knot  in 
the  form  of  an  eight,  each  of  the  wires  passing  through 
one  of  the  loops  of  the  eight.  This  is  a  convenient  method 
of  insulation  for  laboratory  use.  The  two  wires  with 
their  envelope  form  a  small  rod  of  considerable  rigidity 
which  is  easily  slipped  into  apparatus.  With  this  arrange- 
ment it  is  impossible  to  go  above  1200°  or  1300°,  at  which 
temperature  asbestos  melts. 


148 


HIGH   TEMPERATURES. 


For  industrial  instal- 
lations it  is  better  to 
make  use  of  small  fire- 
clay cylinders  of  100 
mm.  in  length  and  10 
mm.  in  diameter,  pierced 
in  .the  direction  of  the 
axis  by  two  holes  of  1  mm. 
diameter,  through  which 
pass  the  wires.  One  or  an- 
other of  the  other  forms 
of  insulator  is  added  in 
sufficient  numbers.  They 
are  placed,  according  to 
the  case,  in  an  iron  tube 
or  in  a  porcelain  tube. 
The  porcelain  tube  should 
be  employed  in  fixed  in- 
stallations in  which  the 
temperatures  may  exceed 
800°.  One  may,  as  does 
Parvillee  in  his  porcelain 
furnaces  (Fig.  32),  place 
the  porcelain  tube  in  the 
lining  of  the  furnace  in 
such  a  way  that  its  end 
is  flush  with  the  inner 
surface  of  the  lining.  An 
open  space  of  a  decimeter 
cube  is  cut  in  the  lining 
about  this  extremity  of 
the  tube.  This  method 
makes  easier  the  estab- 
lishment of  temperature 


THERMOELECTRIC  PYROMETER. 


149 


equilibrium   without   subjecting   the    tube   to   too    great 
chances  of  breaking  by  accidental  blows. 

The  iron  tube  is  used  for  temperatures  not  exceeding 
800°,  in  the  lead  baths  serving  to  temper  steel  for  example, 
and  for  movable  couples  which  are  exposed  to  heat  only 
during  the  time  necessary  to  take  the  observations.  In 
this  case  the  junction  is  placed  some  5  cm.  beyond  the  in- 
sulators and  the  iron  jacket.  The  wires  take  up  the  tem- 
perature within  5  seconds,  and  the  observation  can  be 


FIG.  32. 


FIG.  33. 


taken  before  the  tube  becomes  hot  enough  to  be  burned, 
even  in  furnaces  for  steel  whose  temperatures  exceed 
1600°,  and  before  the  wires  have  had  time  to  be  altered 
even  in  strongly  reducing  flames.  The  other  extremity 
of  the  iron  tube  carries  a  wooden  handle  (Fig.  33)  where 


150  HIGH   TEMPERATURES. 

are  located,  outside,  the  binding-posts  for  the  galvanom- 
eter leads,  and  inside  an  extra  length  of  wire  for  the  couple 
to  replace  portions  burned  or  broken  off.  The  above 
design  gives  the  arrangement  of  this  handle. 

In  all  cases  in  which  the  furnace  whose  temperature  it 
is  desired  to  measure  is  under  a  reduced  pressure,  suitable 
precautions  must  be  taken  to  prevent  any  permanent 
entrance  of  cold  air  by  the  orifice  necessary  for  the  intro- 
duction of  the  tube,  as  well  before  as  during  an  observa- 
tion. Otherwise  one  runs  the  chance  of  having  inexact 
results. 

In  the  case  of  prolonged  observations  in  a  reducing 
atmosphere  or  in  contact  with  melted  bodies,  as  the  metals 
capable  of  altering  the  platinum,  the  couple  should  be 
protected  by  enclosing  it  in  a  covering  impermeable  to  the 
melted  metals  and  to  vapors.  For  fixed  installations  in 
industrial  works  use  should  be  made  of  a  porcelain  tube, 
or  one  of  iron,  closed  at  the  extremity  where  the  junction 
is  located;  in  this  case  the  dimensions  of  the  tube  are  unim- 
portant. For  laboratory  investigations  it  is  indispensable, 
on  the  contrary,  to  have  around  the  wires  a  covering  of  as 
small  diameter  as  possible.  If  it  is  simply  a  question  of 
protecting  the  couple  against  the  action  of  non-volatile 
metals,  the  simplest  way  is  to  use,  as  does  Roberts- Austen, 
a  paste  sold  in  England  under  the  name  of  Purimachos, 
which  serves  to  repair  the  cazettes  employed  in  moulding, 
We  have  made  an  analysis  of  this  which  gave  the  follow- 
ing composition  after  desiccation  at  200°: 

Alumina  and  iron 14 

Soda 3.2 

Water 2.6 

Silica  (by  difference) 80. 2 

It  is  a  very  finely  powdered  quartz  to  which  is  added  10 
per  cent  of  clay,  and  diluted  with  a  solution  of  silicate  of 


THERMOELECTRIC  PYROMETER.  151 

sodium.  To  use  it  the  matter  is  diluted  so  as  to  form  a 
thick  paste,  and  the  couple  is  dipped  in  it  the  required 
length,  arranging  the  wires  parallel  to  each  other  at  a 
distance  apart  of  about  1  mm. 

The  whole  may  then  be  dried  and  calcined  very  rapidly, 
without  fear  of  snapping  the  covering,  as  would  happen 
with  clay  alone;  but  this  covering  is  not  sufficiently  im- 
permeable to  protect  the  couple  against  the  very  volatile 
metals,  as  zinc.  It  is  better,  in  this  case,  to  use  small 
porcelain  tubes  of  5  mm.  inside  diameter,  1  mm.  thick- 
ness of  wall,  and  100  mm.  long,  straight  or  curved  accord- 
ing to  the  usage  to  which  they  are  to  be  put. 

The  couple  insulated  by  asbestos  thread,  or  by  a  small 
inner  porcelain  tube  of  1  mm.  inside  diameter,  as  has  been 
said  previously,  is  pushed  down  to  the  bottom  of  the  tube. 
If  one  has  not  at  hand  such  tubes  of  porcelain,  and  it  is 
required  to  make  a  single  observation  at  a  temperature  not 
exceeding  1000°,  as,  for  instance,  a  standardization  hi  boil- 
ing zinc,  one  may  use  a  glass  tube.  It  melts  and  sticks  to 
the  asbestos,  which  holds  a  thick  enough  layer  to  itself  to 
protect  the  platinum.  But,  on  cooling,  the  tube  breaks, 
and  it  is  necessary  to  make  a  new  set-up  for  each  operation. 
This  is  not  practicable  for  continuous  observations. 

Cold  Junction. — In  general,  in  a  thermoelectric  element, 
one  distinguishes  the  hot  junction  and  the  cold  junction. 
The  latter  is  supposed  kept  at  a  constant  temperature.  In 
order  to  realize  rigorously  this  arrangement,  three  wires 
are  necessary,  two  of  platinum  and  one  of  an  alloy  connect- 
ing two  junctions.  This  theoretical  arrangement  is  practi- 
cally without  interest,  and  the  second  junction  is  always 
dispensed  with.  If,  in  fact,  the  temperature  of  the  whole 
circuit  exclusive  of  the  hot  junction  is  uniform,  the  pres- 
ence or  the  absence  of  the  cold  junction  does  not  affect  the 
electromotive  force;  if  this  temperature  is  not  uniform 


152  HIGH   TEMPERATURES. 

the  second  junction  is  not  advantageous,  for  there  is  then 
in  the  circuit  an  infinity  of  other  junctions  just  as  impor- 
tant to  consider:  the  junctions  of  the  copper  leads  with 
the  platinum  wires,  those  of  the  galvanometer  leads  and  of 
the  different  parts  of  the  galvanometer  among  themselves. 

One  must  satisfy  himself  as  well  as  may  be  as  to  the 
uniformity  of  temperature  in  the  cold  circuit,  and  rigor- 
ously of  the  equality  of  temperature  between  corresponding 
junctions,  particularly  those  of  the  two  platinum  wires  with 
the  copper  leads.  These  uncertainties  in  the  temperature 
of  the  cold  junctions  are  an  important  source  of  error 
in  the  measurement  of  temperatures  by  _  thermoelectric 
couples,  but  for  ordinary  practice  they  are  easily  eliminated. 
In  order  to  realize  exact  measurements,  precise  to  1°, 
for  instance,  it  will  be  necessary  to  have  completely  homo- 
geneous circuits,  including  the  galvanometer,  with  the 
single  exception  of  the  junctions  of  the  platinum  wires 
with  the  conducting  leads;  these  should  be  immersed  in 
the  same  bath  at  constant  temperature.  It  would  be 
necessary  for  this  that  the  constructors  of  galvanometers 
limit  themselves  to  the  use  of  the  same  German  silver  for 
all  parts  of  the  apparatus,  wires  of  the  coil,  suspending  wires, 
leads,  and  parts  of  the  coil.  That  is  difficult  to  obtain. 

In  the  standardization  of  thermocouples  for  exact 
fwork  it  is  customary  to  immerse  the  cold  junctions,  i.e., 
the  points  of  contact  of  the  copper  leads  and  platinum- 
metal  wires,  in  an  oil-bath  in  ice.  With  the  potentiometer, 
irregularities  due  to  other  sources  of  E.M.F.  in  the  cir- 
cuit are  eliminated  by  reversing  simultaneously  the  bat- 
tery current  and  the  couple  circuit. 

Graduation. — There  exist  no  two  couples  possessing 
exactly  the  same  electromotive  force,  although  Heraeus 
has  made  up  several  kilometers  of  pure  platinum  and 
platinum-rhodium  which  give  practically  identical  EJVl.F.s 


THERMOELECTRIC  PYROMETER.  153 

when  made  up  into  couples.  If  it  were  necessary  each 
time  to  make  a  comparison  with  the  air-thermometer, 
this  obligation  would  render  illusory  the  advantages  of  the 
thermoelectric  method.  Practically  one  is  satisfied  to 
make  this  comparison  by  means  of  certain  fixed  points  of 
fusion  and  ebullition.  But  how  many  must  be  taken? 
That  depends  on  the  nature  of  the  function  connectimg 
the  electromotive  force  and  the  temperature. 

Formidce.  —  Avenarius  and  Tait  have  shown  that  up  to 
300°  the  electromotive  force  of  a  great  number  of  couples 
was  represented  in  a  manner  sufficiently  exact  by  means 
of  a  parabolic  formula  of  two  terms: 
e=a(t-tQ)+b(t*-t02). 

The  experiments  of  Le  Chatelier  on  the  platinum-pal- 
ladium couple  have  shown  that  the  same  formula  holds  also 
for  this  couple  up  to  the  fusing-point  of  palladium: 


*  =  100  445  954  1,060  1,550 

e=500  2,950     ^10,900  12,260          24,030 

But  this  law  fails  completely  for  couples  made  of  pure 
platinum  and  an  alloy  of  this  metal. 

Here  are  three  series  of  determinations  made  with  differ- 
ent couples: 


Barus. 

Le  Chatelier. 

Holborn 

and  Wien. 

Pt-Pt 

10%  Ir. 

Pt-Pt 

10%  Rh. 

Pt-Pt 

10%  Rh. 

t 

e 

t 

e 

t 

e 

300 

2,800 

100 

550 

100 

565 

500    • 

5,250 

357 

2,770 

200 

1,260 

700 

7,900 

445 

3,630 

400 

3,030 

900 

10,050 

665 

6,180 

600 

4,920 

1100 

13,800 

1060 

10,560 

800 

6,970 

1550 

16,100 

1000 

9,080 

1780 

18,200 

1200 

11,460 

1400 

13,860 

1600 

16,220 

154  HIGH  TEMPERATURES. 

Holman  has  shown  that  the  results  of  Holborn  and  Wien 
may  be  expressed  by  a  logarithmic  formula  containing 
only  two  parameters.  Le  Chatelier  showed  that  his  re- 
sults could  also  be  represented  by  the  Holman  formula, 
and  in  general  it  may  be  said  that  throughout  the  range 
of  ordinary  use  of  the  thermocouple  the  logarithmic  for- 
mula satisfies  the  results  of  observations  to  2°  C.,  or  well 
within  the  limits  of  all  except  the  most  accurate  work. 

Holman  's  formula  is  as  follows: 


(1) 


where  ^^   e  is  the  electromotive  force  of  the  couple  for 

any  temperature  t  when  the  cold  junction  is  kept  at  zero 
centigrade.  The  two  constants  are  readily  computed 
or  evaluated  graphically,  and  the  resulting  plot  serves 
indefinitely  for  the  determination  of  any  temperature 
with  a  given  couple.  The  equation  does  not  apply  in 
the  region  in  which  the  thermocouple  is  insensitive, 
that  is,  below  250°  C.  It  may  be  written 

(2)  l°g  x.  e=n\og  t+\og  ra; 

•^~*o 

so  that  if  log  e  be  plotted  as  abscissas  and  log  t  as  ordinates, 
a  straight  line  is  obtained. 

The  results  obtained  by  Le  Chatelier  quoted  above 
satisfy  the  equation 

log  e  =  1.2196  log  *  + 0.302; 

e  is  expressed  in  microvolts. 

The  following  table  gives  a  comparison  of  the  results 
observed  with  those  calculated  by  means  of  the  preceding 
formula; 


THERMOELECTRIC  PYROMETER. 


155 


(observed)      (comp.) 


100° 


200 


400 


600 


800 


1000 


1200 


1400 


1600 


e(in 
microvolts) 


log  e       log  e  -  0.3020   log  e  -  0.3020 


102°.  5 

565 

(  +  2.5) 

198.2 

1,260 

(-1.8) 

405 

3,030 

(  +  5) 

602 

4,920 

(  +  2) 

800 

6,970 

(0) 

996 

9,080 

(-4) 

1208 

11,460 

(  +  8) 

1410 

13,860 

(  +  10) 

1603 

16,220 

(+3) 

2.7520        2.4500 


3.1004        2.7984 


3.4814        3.1794 


1.2196 
2.010 

2.927 
2.608 


3.6920        3.3900          2.780 


3.8432        3.5412 


3.9581         3.6561 


4.0591 


3.7571 


4.1418        3.8398 


4.2100        3.9080 


2.903 


2.998 


3.082 


3.150 


3.205 


The  same  formula  has  been  applied  successfully  to  the 
observations  of  Barus  on  platinum-indium  couples. 

Holborn  and  Day  in  their  very  elaborate  direct  com- 
parison of  the  nitrogen-thermometer  with  thermocouples 
made  of  the  various  platinum  metals  find  that  above  250°, 
if  a  precision  of  1°  is  sought,  a  three-term  formula  is  required 
to  express  the  relation  between  E.M.F.  and  temperature. 

The  formula 

'     =-a  +  bt+ct2 


is  the  one  they  have  used.  The  labor  involved  in  com- 
putation with  this  form  is  considerable,  and  unless  a 
very  great  accuracy  is  required  Holman's  formula  is 
amply  sufficient,  when  the  uncertainty  of  the  absolute 
values  of  high  temperatures  is  considered. 

Stansfield  deduces  from  theoretical  considerations  the 
formula    ' 


156  HIGH   TEMPERATURES. 

which  may  be  written 


a  form  which  satisfies  the  experimental  results  determined 
with  pure  platinum  wires.  This  form  possesses  no  prac- 
tical advantage  over  that  of  Holborn  and  Day,  unless  it 
be  its  usefulness,  by  employing  the  graphical  method,  in 

detecting   slight   errors   in  fusing-points.     The  values   of 

j-pi 

-T^Tf  at  the  points  of  fusion  can  be  obtained  from  the  T  vs. 

E  plot,  and  the  T  vs.  -^  curve  thus  constructed  throws 

Cil 

into  prominence  the  experimental  errors  at  these  points. 
As  the  above  formula  indicate,  the  curve  for  the  platinum 

metals   constructed   with    T   as   abscissas   and  T  .  -^   as 

ordinates  is  a  straight  line.  The  errors  of  the  method  are 
less  than  2°  at  1000°.  The  ordinary  metals,  on  the  other 

hand,  give  nearly  a  straight  line  for  the  curve  T  vs.  -^. 

Fixed  Points.  —  The  Holman  formula  includes  only  two 
parameters  which  may  be  determined  by  means  of  two 
observations.  It  will  suffice  therefore  to  have  two  fixed 
points  to  graduate  a  couple,  on  the  condition,  however, 
that  they  be  taken  far  enough  apart.  It  will  be  well  to 
choose  them  in  the  neighborhood  of  the  region  of  tem- 
peratures in  which  the  couple  is  to  be  especially  employed. 
If  two  observations  are  sufficient  theoretically,  it  will  be 
prudent  in  practice  to  utilize  for  the  graduation  a  greater 
number  of  fixed  points  so  as  to  have  a  check  on  the  accu- 
racy of  the  observations.  The  points  to  be  recommended 
by  reason  of  the  a-ccuracy  with  which  they  are  knowTn,  and 
for  their  ease  of  reproduction,  are  the  following: 

Ebullition  of  water; 

Ebullition  of  naphthaline,  or  the  fusion  of  tin; 


THERMOELECrniC  PYROMETER. 


157 


Ebullition  of  sulphur,  or  the  fusion  of  zinc; 

The  fusion  of  gold  or  copper,  or  in  default  the  ebullition 
of  zinc; 

Fusion  of  platinum. 

The  fusing-points  are  easier  to  use  than  the  boiling- 
points  at  temperatures  higher  than  500°.  The  lower 
boiling-points,  water,  naphthaline,  and  sulphur,  can  be 
very  exactly  determined,  but  the  boiling-point  of  zinc  is 
almost  impossible  to  get  well.  The  fusing-points  should 
be  used  above  900°  C. 

For  the  boiling-points  of  water,  naphthaline,  and  sul- 
phur it  is  convenient  to  make  use  of  an  arrangement  due 
to  Barus  (Fig.  34).  This  consists  of  a 
tube  of  thin  glass,  similar  to  test-tubes, 
of  15  mm.  inside  diameter,  300  mm. 
long,  with  a  small  bulb  at  50  mm. 
below  the  open  end.  It  is  surrounded 
with  a  plaster  muff  of  150  mm.  height 
and  100  mm.  diameter  which  has  been 
cast  about  the  glass  tube  inside  of  a 
thin  metallic  cylinder  forming  the  out- 
side surface.  The  bulb  is  immediately 
above  the  plaster  jacket,  below  which 
the  tube,  closed  at  its  lower  end,  ex- 
tends to  a  distance  of  70  mm.  As  soon 
as  the  plaster  has  begun  to  set,  the 
glass  tube  is  taken  out,  giving  it  a 
slight  twisting  motion.  The  cylinder 
is  left  to  dry,  and  the  tube  is  again  put  in 
place.  This  allows,  when  the  tube  is  broken,  of  taking  it 
out  and  replacing  it,  which  would  be  difficult  if  it  adhered  to 
the  plaster.  A  jacketed  Victor  Meyer  tube  may  also  be  used. 

The  lower  free  portion  is  heated  by  a  Bunsen  flame 
gently  at  first,  then  without  any  special  precaution,  once 


FIG.  34. 


158 


HIGH   TEMPERATURES. 


boiling  sets  in.  The  liquid  at  rest  should  occupy  two- 
thirds  of  the  height  of  the  free  end  of  the  tube.  The 
heating  is  .continued  until  the  liquid  coming  from  the 
condensation  of  the  vapor  runs  abundantly  down  the 
walls  of  the  bulb.  The  flame  is  then  adjusted  so  that 
the  limit  of  condensation  of  the  liquid,  which  is  very  sharp, 
remains  constantly  midway  up  the  bulb.  There  is  then 
a  perfectly  uniform  temperature  in  the  interior  cf  the 
glass  tube  throughout  the  height  of  the  plaster  cylinder. 
The  junction  of  the  couple  is  inserted  and  the  coil  of  the 
galvanometer  takes  up  a  fixed  invariable  position.  It  is 
well  to  prevent  the  liquid  from  running  down  about  the 
couple  by  placing  a  small  cone  of  platinum  or  asbestos 
above  the  junction.  Electric  heating  may  also  be  used. 

For  the  boiling-point  of  zinc  Barus  made  small  cruci- 
bles of  porcelain  very  ingeniously  arranged,  but  also  very 
complicated,  besides  being  fragile  and  costly.  One  can 
make  use  more  simply  of  a  porcelain  crucible  70  mm. 
deep  (Fig.  35),  filled  with  melted 
zinc  for  50  mm.  of  its  depth,  and, 
above,  20  mm.  of  charcoal-dust. 
A  cone  pierced  with  a  central  hole 
lets  pass  a  small  porcelain  tube 
containing  the  couple.  The  whole 
is  heated  until  there  is  seen  a  small 
white  flame  of  zinc  escaping  from 
the  crucible.  It  is  indispensable 
that  the  openings  for  the  escape 
of  zinc  vapor  be  large  enough. 
They  tend,  indeed,  to  become 
clogged  by  a  deposit  of  zinc  oxide 
which  solders  at  the  same  time  the 
cover  to  the  crucible,  and  this  causes 
an  explosion  when  there  is  no  longer  vent  for  the  zinc  vapors. 


FIG.  35. 


THERMOELECTRIC  PYROMETER. 


159 


Use  may  be  made  to  advantage  for  this  heating,  and 
still  more  for  the  heating  of  small  crucibles  to  a  very  high 
temperature,  of  a  furnace  model  of  English  make  (Fig.  36), 
which  has  the  advantage  to  resist  almost  indefinitely  the 
action  of  heat  and  to  be  very  easily  repaired.  The  princi- 
ple of  the  construction  of  these  furnaces  is  to  make  them 
of  two  concentric  layers.  The  outer  covering  of  fire-clay, 
bound  together  by  iron,  gives  solidity  to  the  furnace;  it 
receives  but  indirectly  the  action  of  the  heat,  and  is  not 
exposed  to  cracking  by  shrinkage  under  the  action  of  too 
high  temperatures.  The  inner  envelope,  which  alone 
receives  the  action  of  the  heat,  is  made  of  large-grained 
quartz  sand,  grains  of  1  mm.,  mixed  with  a  small  amount 
of  a  flux.  At  a  high  temperature  the  quartz  does  not 
shrink  as  does  clay;  it  expands,  on  the  contrary,  passing 
over  to  the  form  of  amorphous  silica  with  a  change  of 
density  from  2.6  to  2.2.  But  this  transformation  is  effected 
only  with  extreme  slowness,  otherwise  it  would  burst  the 
furnace.  If  by  chance  this  inner  lining  falls  down,  it  is 


FIG.  36. 

easily  replaced  by  putting  into  the  furnace  a  glass  jar  of 
suitable  diameter,  surrounded  with  a  sheet  of  oiled  paper, 
and  packing  about  this,  coarse  quartz  sand  slightly  mois- 


160  HIGH   TEMPERATURES. 

tened  with  a  sirupy  solution  of  alkaline  silicate.  The 
furnace  is  heated  by  means  of  a  lateral  opening  with  a 
Fletcher  lamp,  which  has  the  advantage  -of  being  sturdy, 
or  with  an  ordinary  blast-lamp. 

In  the  use  of  fusing-points  there  are  several  cases  to 
distinguish.  If  one  wishes  to  employ  a  considerable  quan- 
tity of  metal,  as  with  zinc,  lead,  and  tin,  the  easiest  way 
is  to  melt  them  in  a  crucible,  into  which  is  thrust  the 
properly  protected  couple,  and  let  the  whole  cool.  There 
is  observed  with  ho  difficulty  the  stationary  temperature 
of  solidification. 

If  only  a  small  quantity  of  metal  can  be  employed,  as  in 
the  case  of  gold,  or  if  there  is  no  installation  for  heating 
the  crucibles,  it  is  possible  to  obtain  the  fusing-points  as 
follows:  One  wraps  about  the  junction,  so  as  to  cover  it 
completely,  a  fine  wire  of  the  metal  chosen  (it  suffices  with 
a  little  practice  to  use  but  a  centigramme  of  metal),  and 
then  places  the  couple  in  an  enclosure  at  stationary  tem- 
perature slightly  higher  than  that  of  fusion,  or  at  tem- 
perature increasing  very  regularly.  The  galvanometer 
readings  are  noted,  which  at  the  instant  of  fusion  show  a 
momentary  halt  followed  by  a  sudden  jump.  But  this 
perturbation  is  the  more  feeble  the  smaller  the  metallic 
mass,  and  a  certain  practice  is  necessary  in  this  kind  of 
observation  in  order  to  seize  with  certainty  the  halting- 
point.  It  is  evident  that  the  heating  must  be  absolutely 
regular.  It  is  impossible  to  obtain  this  result  with  a  free 
flame,  which  is  always  unsteady.  In  order  to  have  a 
stationary  temperature,  use  is  made  in  the  laboratory  of 
a  tube  or  a  muffle  placed  in  a  furnace  that  has  been  lighted 
for  some  time;  at  industrial  works,  a  chimney  or  flue  for 
the  escape  of  smoke.  In  these  enclosures  the  temperature 
varies  from  spot  to  spot,  and  one  can,  after  a  few  trials 
find  the  proper  temperature.  In  order  to  work  at  increas- 


THERMOELECTRIC  PYROMETER. 


161 


ing  temperatures,  which  is  the  most  convenient  in  the 
laboratory,  the  junction  is  placed,  properly  prepared,  in 
a  little  crucible  filled  with  powdered,  non-fusible,  poor 
conducting  material,  or  else  the  junction  is  simply  wrapped 
in  a  bullet  of  plaster,  clay,  or  Purimachos.  Care  is  taken 


iSW 

1600 
1400 
1200 
1000 
800 
GOO 
400 
200 

( 

I 

/ 

/ 

Pt(l779°). 

Au  (1065°) 
Zn(925°ebumtion) 

Al(655°) 

S   (445) 
Zn  (420°  fusion) 

CiOH"(218°) 
H«O(100°) 

/ 

/ 

/ 

/ 

/ 

/ 

A/ 

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. 

//(£) 

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x 

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^/X 

1 

j            20           40           60           80          100          120         140   150  mm  (l) 
I             5            10           15           20           25           30           35    37.5  divisions  (2) 
1            40           80          120          160         200         j24JJ,        280   SOOmniQS) 

FIG.  37. 

to  begin  by  drying  and  dehydrating  slowly  this  bullet 
to  prevent  its  bursting.  It  is  then  placed  in  a  flame 
sufficiently  hot  to  bring  about  fusion  of  the  metal;  this 
flame  should  be  very  steady. 

For  the  fusion  of  platinum  a  different  process  should  be 
followed.  One  utilizes  the  fusion  of  the  wires  of  the 
couple  in  the  same  operation  which  serves  to  make  the 


162  HIGH   TEMPERATURES. 

junction.  Two  observers  are  necessary,  one  to  read  the 
galvanometer  and  the  other  to  note  the  fusion  of  the 
platinum.  It  is  necessary  to  employ  a  flame  sufficiently 
tall  so  that  the  temperature  be  regular  throughout  a  con- 
siderable height.  The  junction  of  the  two  twisted  wires 
is  placed  at  a  distance  of  at  least  50  mm.  above  the  blast- 
lamp  nozzle,  a  strong  blast  of  oxygen  is  turned  on,  and 
the  gas-cock  is  opened  gradually  until  fusion  takes  place. 
The  same  process  should  be  used  for  the  fusion  of  gold, 
with  an  air  blast-lamp,  on  the  condition  that  the  flame  of 
the  latter  be  kept  steady,  which  is  not  possible  with  bel- 
lows worked  by  foot.  This  method  is,  h  ver,  less  precise 
than  those  that  have  been  previously  indicated. 

We  give  here  the  curves  of  graduation  (Fig.  37)  of 
different  couples,  attached  to  different  galvanometers  or, 
in  the  case  of  the  method  of  opposition  (Poggendorf's 
method),  to  a  Pouillet  rheostat.  In  the  last  case  the  zero 
of  graduation  does  not  correspond  to  a  zero  electromotive 
force,  and  in  consequence  not  to  "the  temperature  of  the 
surrounding  air,  by  reason  f  the  supplementary  resist- 
ance of  a  wire  which  was  added  to  that  of  the  rheostat. 

Fixed  Mirror  Pointer          Method  of 

Points.  Galvanometer.  Galvanometer.  Opposition. 

Boiling  water 100°       4 . 5  divs. 

Boiling  naphthaline ..  218      12        "  2.5  divs.       13mm. 

Melting  zinc 420      26        " 

Boiling  sulphur 445      28        "  123      " 

Melting  aluminium.  . .  655  12      divs. 

Boiling  zinc 925      64      divs 294      " 

Melting  gold 1065  20      divs. 

Melting  platinum 1780  137.5  divs,  37 

Recent  Researches. — The  reliability  of  Holman's  formula 
may  also  be  illustrated  by  comparing  his  determinations 
of  certain  fixed  points  with  more  recently  found  values. 


THERMOELECTRIC  PYROMETER.  163 

The  two  fixed  points  assumed  by  Holman,  in  his  work 
with  Lawrence  and  Barr,  were  the  sulphur-point  and  the 
gold-point.  Taking  the  S.B.P.=445  and  the  gold-point 
=  1064,  Holman 's  values  of  other  points  become,  using 
his  formula, 

Al  Ag  Cu  Pt 

654.7  962.7  1087  1760 

The  values  determined  by  Holborn  and  Day  are 

Al  Ag  Cu  Au 

657  to  654         961 . 5  1084  1064 

These  results  should  also  be  compared  with  Stansfield's, 
who  worked  with  a  Roberts-Austen  recording-pyrometer, 
which  he  rendered  still  more  sensitive  by  means  of  an 
auxiliary  potentiometer,  which  balances  the  major  part 
of  the  E.M.F.  of  the  couple,  the  sensitive  galvanometer 
being  acted  upon  by  only  a  small  fraction  of  the  thermo- 
current.  The  cold  junction  was  kept  in  boiling  water. 
He  obtained 

Al  Ag  Cu  Au 

649.2  961.5  1083  1063 

All  of  the  above  results  go  to  show  that  the  thermo- 
couple, made  of  relatively  pure  materials  obtained  from 
various  sources,  used  under  the  most  diverse  experimental 
conditions,  and  its  indications  reduced  by  different  methods, 
will  nevertheless  give  results  agreeing  to  0.5  per  cent  or 
even  closer  over  the  range  within  which  the  thermo- 
couple can  be  used. 

Electric  Heating. — In  recent  years  a  great  advance  has 
been  made  in  pyrometric  practice  in  substituting  for  gas 


164  HIGI}   TEMPERATURES. 

furnaces  those  employing  electric  heating.  This  method 
was  first  used  in  pyrometric  work  for  the  determination 
of  fixed  points  by  means  of  the  thermocouple  by  D.  Ber- 
thelot  in  France  and  liolborn  and  Day  in  Germany. 
The  earlier  furnaces  were  constructed  by  winding  pure 
nickel  or  platinum  wire  on  porcelain  tubes  enclosed  in  an 
outer  tube  of  porcelain  and  wrapped  in  asbestos.  The 
nickel- wound  furnaces  may  be  used  up  to  1300°  C.  with 
care  and  they  are  readily  rewound  when  burnt  out.  The 
platinum-wire  furnaces  are  very  expensive,  but  may  be 
used  up  to  1500°  C.  These  last  have  since  been  displaced 
by  furnaces  of  the  Heraeus  type,  which  are  made  by  wind- 
ing platinum-/oi2  of  about  0.007  mm.  thickness  on  por- 
celain tubes  covered  with  an  aluminium  earth  paste  which 
does  not  attack  platinum  at  high  temperatures.  These 
furnaces  are  inexpensive  and  very  durable.  Heraeus  also 
manufactures  iridium  resistance  furnaces  with  which  tem- 
peratures over  2000°  C.  may  be  reached,  and  a  very  con- 
stant temperature  maintained.  A  further  advantage  of 
the  electric  furnace  is  the  absence  of  reducing  gases. 

The  use  of  electric  heating  has  rendered  the  standard- 
ization of  the  thermocouple  and  all  other  pyrometers  an 
easy  matter  and  increased  greatly  the  accuracy  attain- 
able in  establishing  the  fixed  points  in  pyrometry. 

Holborn  and  Day's  Work. — In  a  series  of  painstaking 
researches  carried  out  at  the  Reichsanstalt,  these  physi- 
cists, using  electric  heating,  have  succeeded  in  establish- 
ing many  of  the  fixed  points  more  exactly  than  had  been 
previously  done.  We  shall  return  to  their  work  again  in 
the  chapter  on  standardization.  They  determined  several 
points  by  two  methods  which  they  call  the  wire  method 
and  the  crucible  method.  The  former  consists  in  insert- 
ing in  the  thermoelectric  circuit  between  the  platinum 


THERMOELECTRIC  PYROMETER.  165 

and  platinum-rhodium  a  centimeter  of  the  wire  (less  than 
0.03  gr.)  of  the  material  whose  melting-point  is  sought, 
the  junction  thus  modified  being  heated  in  an  electric 
furnace  until  the  metal  melts,  the  E.M.F.  being  noted  as 
the  circuit  breaks.  With  the  crucible  method  a  large 
mass — several  hundred  grammes  at  least — is  heated  in 
a  crucible  placed  at  the  center  of  an  electric  furnace, 
whose  temperature  may  be  so  nicely  controlled  that  the 
freezing  of  300  grm.  of  gold  or  copper,  for  instance, 
will  take  an  hour  or  more.  Both  graphite  and  porcelain 
crucibles  were  used  to  test  the  effects  of  reducing  and 
oxidizing  surroundings.  The  metal  in  the  graphite 
crucible  is  also  covered  with  powdered  graphite.  The 
wire  and  crucible  methods  gave  identical  results  with 
gold,  whose  melting-point  they  find  to  be  1064.0  ±0°. 6  C. 
Copper  wire  in  air  gave  1065,  so  that  either  a  copper  or 
gold  wire  may  be  used  to  establish  the  same  fixed  point. 
Copper  in  graphite  gives  the  freezing-point  of  1084,  how- 
ever. The  convenience  of  the  wire  method  is  offset  by  the 
contamination  of  the  junction. 

If  a  thermocouple,  however  well  protected,  is  heated 
for  a  long  time  at  a  high  temperature,  its  E.M.F.  will 
change.  It  is  well  for  accurate  work  to  have  at  least  two 
thermocouples,  one  of  which  is  kept  as  a  standard  and 
only  occasionally  heated  and  never  above  1200°  C.  In 
this  way  changes  in  the  couple  ordinarily  used  may  be 
readily  detected.  Holborn,  with  Henning  and  Austin, 
has  made  a  very  complete  study  of  the  effects  of  continued 
heating  in  various  atmospheres  on  the  loss  of  weight 
and  changes  produced  in  electric  and  thermoelectric 
properties  of  the  platinum  metals.  The  following  table 
shows  the  results  of  continued  heating  in  air  on  the  E.M.F. 
of  the  couples  ordinarily  used: 


166 


HIGH   TEMPERATURES. 


EFFECT    OF    PROLONGED    HEATING    ON    E.M. 
E.M.F.    AGAINST    PT    IN    MICROVOLTS. 


Duration  of 

90  Pt—  10  Ir. 

Heating, 

Hours. 

700°  C. 

900° 

1100° 

1300° 

0 



16,540 

19,740 

3 

9460 

12,450 

15,450 

18,530 

f    6 

9160 

11,930 

14,780 

17,640 

LS 

8840 

11,560 

14,300 

17,050 

90  Pt—  10  Rh. 

800°  C. 

900° 

1000° 

1100° 

0 

7230 

8340 

94SO 

10,670 

3 

7250 

8380 

9510 

10,690 

6 

7270 

8400 

9540 

9 

7280 

8410 

9540 

10,720 

12 

7290 

8420 

9550 

This  investigation  shows  that  the  E.M.F.  of  a  couple, 
and  thus  the  indicated  temperature,  rise  with  continued 
heating,  very  considerably  for  a  Pt — Ir  couple  and  about 
0.5  per  cent  for  a  Pt — Rh  couple  for  ten  hours'  heating. 
The  change  is  greatest  during  the  first  part  of  the  heating. 
Before  use,  a  thermocouple  should  be  annealed  by  passing 
a  current  through  it  at  a  white  heat,  when  future  changes 
will  be  slight.  This  annealing  also  will  restore  to  very 
nearly  its  normal  value  the  E.M.F.  of  couples  which 
have  been  in  contact  with  silicates. 

Changes  in  temperature  distribution  along  the  wire  will 
also  affect  the  apparent  electromotive  force  of  the  couple, 
causing  apparent  changes  in  temperature  as  great  as  20° 
at  1000°  C.  with  the  best  wires  obtainable.  The  less 
homogeneous  the  wires  the  more  marked  is  this  effect. 


THERMOELECTRIC  PYROMETER.  167 

In  the  most  exact  work,  therefore,  the  same  conditions 
of  immersion  must  be  followed  throughout,  or  the  result- 
ing changes  in  E.M.F.  measured. 

It  follows  from  all  this,  as  Holborn  and  Day  state,  that 
the  temperature  scale,  once  established,  by  means  of  the 
thermocouple,  can  be  maintained  with  certainty  only 
with  the  help  of  fixed  temperatures  such  as  the  melting- 
points. 

Industrial  Applications. — The  measurement  of  tempera- 
tures by  thermoelectric  couples  has  enhanced  the  accurate 
knowledge  of  a  great  number  of  high  temperatures  of 
which  previously  little  or  nothing  was  known.  The 
measurements  have  been  particularly  numerous  in  the 
scientific  and  industrial  investigations  on  iron.  It  is  with 
the  thermoelectric  couple  that  Osmond  and  others,  Roberts- 
Austen,  Arnold,  Howe,  and  Charpy  have  made  all  their 
studies  on  the  molecular  transformations  of  irons  and 
steels.  The  conditions  of  manufacture  and  of  treatment 
of  these  metals  have  been  improved  by  the  introduction 
into  industrial  works  of  this  method  of  high-temperature 
measurements. 

We  give  below,  as  examples,  a  series  of  determinations 
made  by  Le  Chatelier  in  a  certain  number  of  industrial 
operations. 

Steel. — Siemens-Martin  open-hearth  furnace: 

Gas  at  the  outlet  of  the  gas-generator 720° 

Gas  at  the  entrance  of  the  regenerator 400 

Gas  at  the  outlet  of  the  regenerator 1200 

Air   "     "        "       "     "             "         1000 

Interior  of  the  furnace  during  refining 1550 

Smoke  at  the  foot  of  the  chimney 300 

Glass. — Basin  furnace  for  bottles;  pot  furnace  for 
window-glass : 


168  HIGH   TEMPERATURES. 

Furnace 1400° 

Glass  in  affinage 1310 

Annealing  of  bottles 585 

Drying  of  window-glass 600 

Illuminating-gas.- — Gazogene  furnace : 

Top  of  furnace 1190° 

Base  of  furnace 1060 

Retort  at  end  of  distillation 975 

Smoke  at  base  of  regenerator 680 

Porcelain. — Furnaces : 

Hard  porcelain 1400° 

China  porcelain 1275 

Conditions  of  Use. — Thermoelectric  couples,  by  reason 
of  their  easy  use,  ready  calibration,  small  size,  and  of  the 
precision  of  their  indications,  are  preferable  to  all  other 
pyrometric  methods  for  ordinary  investigations,  scientific 
or  industrial,  and  in  fact  they  are  almost  the  only  ones 
employed  to-day  for  such  uses.  Their  employment,  how- 
ever, is  not  to  be  recommended  for  investigations  of  the 
highest  precision;  the  preference  should  be  given,  as  we 
have  already  said,  to  the  electric-resistance  pyrometer, 
within  the  range  that  this  instrument  can  be  used, 
when  one  possesses  the  means  to  graduate  it  with  precision 
up  to  high  temperatures.  Above  1000°  C.  the  thermo- 
couple is  the  only  form  of  electrical  pyrometer  which  can 
be  used;  and  attached  to  a  suitable  direct-reading  gal- 
vanometer, this  instrument  is  proving  of  great  utility 
in  the  industries.  In  certain  cases,  which  wre  shall  dis- 
cuss, a  radiation  or  optical  pyrometer  may  replace  to 
advantage  the  thermoelectric. 

Indium-ruthenium  Couple  of  Heraeus. — The  upper 
limit  for  continued  use  of  the  platinum-rhodium  couple  is 


THERMOELECTRIC  PYROMETER.  169 

about  1600°  C.  If  a  couple  could  be  made  of  more  refrac- 
tory metals,  higher  temperatures  might  be  measured. 
This  has  just  been  accomplished  by  Heraeus  using  a  couple 
composed  of  pure  iridium  for  one  lead,  and  for  the  other 
an  alloy  of  90  parts  iridium  to  10  parts  ruthenium,  whose 
indications  reach  2100°  C. 

Such  a  couple  may  be  calibrated  hi  terms  of  a  rhodium 
couple  up  to  1600°  and  the  platinum  fusing-point  may  be 
taken  by  the  wire  method  as  a  higher  fixed  point  (1780°), 
but  for  still  higher  temperatures  extrapolation  of  the 
E.M.F. -temperature  relation  must  be  resorted  to. 

Heraeus  gives  the  following  calibration  of  such  a  couple: 

900° C..  .2.95  millivolts 


1000 

3.32 

1100 

3.70 

1200 

4.08 

1300 

;..:  4.43 

1400 

4.78 

1500 

5.07 

1600 

5.32 

1700 

...¥  5.58 

1780 

5.75 

1800 

5.79 

1900 

;.  5.99 

2000 

6.18 

2100 

.  6.36 

The  indications  of  this  couple  remain  very  constant 
with  repeated  heatings.  The  effect  of  heat  conduction 
along  the  leads  may  cause  an  error  as  great  as  50°,  but 
this  is  readily  eliminated  by  taking  the  platinum  point. 

The  iridium-ruthenium  couple  has  to  be  handled  very 
carefully  as  it  is  eccessively  brittle. 

Furnaces  suitable  for  these  high  temperatures  may  be 


170  HIGH   TEMPERATURES. 

made  of  chalk,  magnesia,  or  iridium  heated  with  an  oxy- 
hydrogen  flame.  When  chemical  action  is  feared  or  com- 
plete freedom  from  gases  is  desired,  an  electrically  heated 
iridium-tube  furnace,  also  due  to  Heraeus,  may  be  used. 

Such  iridium  tubes  as  made  by  Heraeus  have  walls  0.2 
to  0.3  mm.  thick  and  carry  from  500  to  1000  amperes 
at  low  voltage. 


CHAPTER  VII. 
THE  LAWS  OF  RADIATION. 

General  Principles. — The  temperature  of  bodies  may 
be  estimated  from  the  radiant  energy  that  they  send  out, 
either  in  the  form  of  visible  light  radiation  or  of  the  longer 
infra-red  waves  that  are  studied  by  their  thermal  effects. 
For  the  estimation  of  temperature  in  this  way  use  is  made 
of  the  so-called  laws  of  radiation. 

Temperature  and  Intensity  of  Radiation. —  When  we 
consider  the  enormous  increase  in  the  intensity  of  radia- 
tion with  rise  in  temperature,  this  method  appears  espe- 
cially well  adapted  to  the  measurement  of  high  tem- 
peratures. Thus,  for  example,  if  the  intensity  of  the 
red  light  (A =0.65^)  emitted  by  a  body  at  1000°  C.  is 
called  1,  at  1500°  C.  the  intensity  will  be  over  130  times 
as  great,  and  at  2000°  C.  over  2100  times  as  great. 

The  rapid  increase  of  the  photometric  intensity  of  the 
light  in  comparison  with  that  of  the  temperatures  is  shown 
by  the  following  table,  from  Lummer  and  Kurlbaum, 
for  light  emitted  by  incandescent  platinum.  If  7t  and  72 
are  the  intensities  of  the  light  emitted  at  the  absolute 
temperatures  Tl  and  T2  (not  differing  many  degrees  from 
one  another),  then  if  we  write 


171 


172  HIGH  TEMPERATURES. 

The  values  of  x  at  various  absolute  temperatures  (T°  C. 
+273°)  are  as  follows: 

T°  abs.  x. 

900°  30 

1000  25 

1100  21 

1200  19 

1400  18 

1600  15 

1900  14 

From  this  table  it  will  at  once  be  seen  that  at  1000° 
absolute  (727°  C.)  the  intensity  of  the  light  increases 
twenty-five  times  as  rapidly  as  the  temperature;  at 
1900°  absolute  (1627°  C.)  fourteen  times  as  rapidly. 
The  product  Tx= 25000  as  shown  by  Rasch  seems  to 
express  the  relation  between  T  and  the  exponent  x. 

Emissive  Powers. — It  would  therefore  appear  that  a 
system  of  optical  pyrometry  based  on  the  intensity  of 
the  light  emitted  by  incandescent  bodies  would  be  an 
ideal  one,  inasmuch  as  a  comparatively  rough  measure- 
ment of  the  photometric  intensity  would  measure  the 
temperature  quite  accurately.  This,  however,  is  only 
partly  true;  it  is  limited  somewhat  by  the  fact  that  differ- 
ent bodies,  although  at  the  same  temperature,  emit  vastly 
different  amounts  of  light.  Thus  the  intensity  of  the 
radiation  from  incandescent  iron  or  carbon  at  1000°  C., 
for  example,  is  many  times  greater  than  that  emitted  by 
such  substances  as  magnesia,  polished  platinum,  etc., 
at  the  same  temperature.  Consequently,  if  any  con- 
clusions were  drawn  as  to  the  temperatures  of  these  bodies 
from  the  light  that  they  emit,  it  might  lead  to  large  errors. 
Thus  at  1500°  C.  this  difference  in  the  intensity  of  the 
light  emitted  by  carbon  and  by  polished  platinum  would 


THE  LAWS  OF  RADIATION.  173 

lead  to  a  difference  in  the  estimated  temperature  of  these 
bodies  of  about  100°  C.,  and  less  at  lower  temperatures. 

The  "  Black  Body  "  of  Kirchoff. — Kirchoff  in  one  of  the 
most  important  contributions  to  the  theory  of  radiation 
was  led  to  the  important  conception  of  what  he  termed 
a  "black  body,"  which  he  defined  as  one  which  would 
absorb  all  radiations  falling  on  it,  and  would  neither 
reflect  nor  transmit  any.  He  further  pointed  out  clearly 
the  important  fact  that  the  radiation  from  such  a  black 
body  was  a  function  of  the  temperature  alone,  and  was 
identical  with  the  radiation  inside  an  enclosure  all  parts 
of  which  have  the  same  temperature.  The  first  experi- 
mental realization  of  a  black  body  as  a  practical  laboratory- 
apparatus  was  made  by  Lummer  and  Wien,  by  heating 
the  walls  of  a  hollow  opaque  enclosure  as  uniformly  as 
possible  and  observing  the  radiation  coming  from  the 
inside  through  a  very  small  opening  in  the  walls  of  the 
enclosure. 

Experimental  Realization. — No  body  is  known  whose  sur- 
face radiation  is  exactly  that  of  a  black  body.  The  radia- 
tions from  such  substances  as  carbon  and  iron  approximate 
fairly  near  to  black-body  radiation,  while  such  bodies  as 
polished  platinum  and  magnesia,  etc.,  depart  very  far 
from  it.  Black-body  radiations  corresponding  to  tem- 
peratures from  that  of  liquid  air  or  lower,  up  to  1600°  C. 
or  higher  (if  suitable  materials  are  chosen),  are  now  avail- 
able in  the  laboratory.  For  temperatures  up  to  600° 
or  thereabouts,  this  is  realized  by  immersing  a  metallic 
or  other  vessel  in  a  constant  temperature  bath  (liquid 
gas,  vapor,  or  fused  salt)  and  observing  the  radiation  from 
the  interior  through  a  small  opening  in  the  walls.  At 
higher  temperatures  it  is  very  difficult  to  heat  the  walls 
of  the  enclosure  uniformly,  especially  with  gas-flames. 
Lummer  and  Kurlbaum  have  very  satisfactorily  overcome 


man  TEMPERATURES. 


THE  LAWS  OF  RADIATION.  175 

this   difficulty   in    their   electrically   heated   black   body 
which  is  shown  in  section  in  Fig.  38. 

The  central  porcelain  tube  is  wound  over  with  thin 
platinum-foil  through  which  an  electric  current  is  sent 
which  can  be  adjusted  to  maintain  any  desired  tempera- 
ture up  to  1600°  C.  This  tube  is  provided  with  a  number 
of  diaphragms  to  minimize  the  disturbing  effects  of  air- 
currents.  To  protect  this  inner  tube  from  external  in- 
fluences and  to  diminish  unnecessary  heat  losses,  it  is 
surrounded  by  several  porcelain  tubes  and  air-spaces,  as 
shown  in  the  figure.  The  radiation  from  the  uniformly 
heated  region  near  the  centre  and  which  passes  out  through 
the  end  of  the  tube  at  0  is  a  very  close  approximation  of 
the  ideal  black-body  radiation  of  Kirchoff.  The  tempera- 
ture of  this  central  region  is  measured  by  means  of  a  care- 
fully calibrated  thermocouple. 

As  has  already  been  stated,  if  magnesia,  porcelain,  plati- 
num, iron,  etc.,  are  heated  to  the  same  temperature,  they 
will  emit  vastly  different  amounts  of  light.  If,  however, 
these  bodies  *  are  heated  inside  a  black  body,  they  will 
all  emit  the  same  radiation,  and  on  looking  into  the  small 
opening  all  details  of  their  contour  will  be  lost,  the  whole 
region  being  of  uniform  brightness.  Thus,  in  the  black 
body  described  above,  before  the  heating  has  become 
uniform,  the  platinum  wires  of  the  thermocouple  can  be 
seen  as  dark  lines  against  the  brighter  background,  but 
when  the  heating  current  has  been  maintained  constant 
for  some  time,  so  that  the  heating  has  become  uniform 
hi  the  inner  central  chamber,  the  wires  of  the  couple  almost 
completely  disappear,  notwithstanding  that,  of  all  sub- 

*It  is  here  assumed  that  the  radiation  is  purely  thermal  and 
that  no  part  is  due  to  luminescence,  as  the  laws  of  radiation  are 
only  directly  applicable  where  such  is  the  case. 


176  HIGH  TEMPERATURES. 

stances,  platinum  and  the  black  oxide  of  the  radiating  walls 
differ  most  widely  in  their  radiating  powers  (emissivities). 

Realization  in  Practice.  —  Fortunately  in  pyrometric 
practice  it  is  often  easy  to  realize  very  nearly  the  condi- 
tions of  a  black  or  totally  absorbing  body.  Thus  the 
interior  of  most  furnaces,  kilns,  and  ovens  approximates 
this  condition,  or  the  bottom  of  a  closed  tube  of  any 
material  thrust  into  any  space  heated  to  incandescence. 
Again,  iron  and  coal  observed  in  the  open  are  not  far 
removed  in  their  optical  properties  from  the  black  body. 

Black-body  Temperature.  —  The  term  black-body  tem- 
perature has  come  into  quite  extensive  use  and  is  of  great 
convenience  in  the  discussion  of  pyrometric  problems. 
The  temperatures  indicated  by  a  radiation-pyrometer  that 
has  been  calibrated  against  a  black  body  are  known  as 
black-body  temperatures.  Thus,  were  a  piece  of  iron  and 
a  piece  of  porcelain  both  at  1200°,  the  optical  pyrometer, 
which  used  the  red  light  emitted  by  these  bodies,  would 
give,  as  the  temperature  of  these  bodies,  1140°  and  1100° 
respectively.  This  means  that  iron  and  porcelain  at  1200° 
emit  red  light  of  the  same  intensity  as  is  emitted  by  a 
black  body  at  1140°  and  1100°  C.  respectively.  The 
"black-body  temperature"  of  these  materials  for  green 
light  might  differ  quite  appreciably  from  that  for  red 
light.  It  is  at  once  evident  that  if  the  "black-body  tem- 
peratures" of  different  bodies,  e.g.,  carbon  and  platinum, 
are  equal,  their  actual  temperatures  may  differ  consider- 
ably (180°  C.,  or  so,  at  1500°  C.).  This  violates  our  ordi- 
nary conception  of  equal  temperatures,  which  is  based 
on  thermal  equilibrium  between  the  bodies  if  brought 
into  contact. 

The  temperature  of  any  body,  therefore,  as  measured 
by  an  optical  pyrometer :~~wills  always  be  lower  than  its 
true  temperature  by  an  amount  depending  on  the  depar- 


THE  LAWS  OF  RADIATION.  177 

ture  of  its  radiation  from  that  of  a  black  body.  There 
is  another  source  of  error,  however,  that  may  act  in  the 
direction  of  making  the  pyrometer  read  too  high,  due 
to  light  reflected  by  the  body  whose  temperature  is  being 
measured.  This  source  of  error  may  very  often  be  elimi- 
nated, where  the  accessibility  of  the  work  permits,  by 
running  a  tube  down  to  the  incandescent  surface,  which 
will  cut  off  stray  radiation  from  the  surrounding  flames. 
The  magnitude  of  the  error  that  may  arise  from  light 
reflected  from  surrounding  hotter  objects  may  be  quite 
considerable  (several  hundred  degrees),  depending  on  the 
temperature,  area,  and  position  of  the  surrounding  hot 
objects  and  the  reflecting  power  of  the  surface  whose 
temperature  is  under  observation. 

LAWS    OF  RADIATION. 

Stefan's  Law. — Naturally  the  first  relation  sought 
between  intensity  of  radiation  and  temperature  was  one 
for  the  total  radiation  energy  sent  out  by  a  body,  as  it 
required  less  delicate  instruments  for  measurement  than 
the  study  of  the  spectral  distribution  of  energy.  Numer- 
ous attempts  to  express  such  a  relation  were  made  by 
Newton,  Dulong  and  Petit,  Rosetti,  and  others.  These 
attempts,  however,  merely  resulted  in  empirical  expres- 
sions that  held  only  through  narrow  ranges  of  tempera- 
ture. The  first  important  step  was  made  by  Stefan,  who 
examined  some  of  the  experimental  data  of  Tyndall  on 
the  radiation  of  incandescent  platinum  wire  in  the  inter- 
val 525°  C.  to  1200°  C.,  and  was  led  to  the  conclusion 
that  the  energy  radiated  was  proportional  to  the  fourth 
power  of  the  absolute  temperatures.  This  relation  seemed 
to  be  further  supported  by  the  best  experimental  data 
of  other  observers,  at  least  to  within  the  limit  of  accuracy 
of  their  observations,  being  strictly  true,  however,  only 


178 


HIGH   TEMPERATURES. 


for  the  energy  of  total  radiation  from  a  black  body.  This 
relation  received  independent  confirmation  from  Boltz- 
mann,  who  deduced  it  from  therm  odynamic  reasoning. 
The  conditions  imposed  by  Boltzmann  in  his  discussion 
on  the  nature  of  the  radiation  were  such  as  are  fulfilled 
by  the  radiation  from  a  black  body.  This  relation,  which 
has  now  come  to  be  generally  known  as  the  Stefan-Boltz- 
mann  radiation  law,  may  then  be  stated  as  follows: 

The  energy  radiated  by  a  black   body  is  proportional  to 
the  fourth  power  of  the  absolute  temperature,  or 


when  E  is  the  total  energy  radiated  by  the  body  at  abso- 
lute temperature  T°  to  the  body  at  absolute  temperature 
Tr0°,  and  K  is  a  constant  depending  on  the  units  used. 
This  law  has  received  abundant  experimental  support  from 
the  researches  of  Lummer,  Kurlbaum,  Pringsheim,  Paschen, 
and  others,  throughout  the  widest  range  within  which 
temperature-measurements  can  -be  made. 

An  illustration  of  the  experimental  evidence  in  support 
of  this  law  is  given  in  the  table  taken  from  the  experi- 
ments of  Lummer  and  Kurlbaum: 


Absolute  Temperature. 

K 

T 

To 

Black  body. 

Polished 
Platinum. 

Iron  Oxide. 

372.8 

290.5 

108.9 

492 

290 

109.0 

2.28 

33.1 

654 

290 

108.4 

6.56 

33.1 

795 

290 

109.9 

8.14 

36.6 

1108 

290 

109.0 

12.18 

46.9 

1481 

290 

110.7 

16.69 

65.3 

1761 

290 

19.64 

.... 

THE  LAWS  OF  RADIATION  179 

It  will  also  be  seen  from  this  table  that  while  the  intensity 
of  the  total  radiation  of  iron  oxide  is  4  or  5  times  that  of 
polished  platinum,  it  is  still  considerably  less  than  that 
emitted  by  a  black  body.  The  total  radiation  from 
bodies  other  than  a  black  body  increases  more  rapidly 
than  the  4th  power  of  the  absolute  temperature,  so  that 
as  the  temperature  is  raised  the  radiation  of  all  bodies 
approaches  that  of  the  black  body. 

Laws  of  Energy  Distribution. — Among  the  first  facts 
to  be  noticed  about  the  nature  of  the  radiations  sent  out 
by  bodies  were,  that  at  low  temperatures  these  radiations 
consisted  of  ether  waves  too  long  to  affect  the  human 
eye.  As  the  temperature  was  raised,  shorter  and  shorter 
waves  were  added  which  could  finally  be  detected  by  the 
eye;  the  first  of  the  visible  radiajgns  producing  the 
sensation  termed  red,  then  orange,  ^f ,  until  the  violet 
waves  were  reached,  which  were  the  shortest  waves  that 
the  eye  could  detect. 

Soon  after  Langley  brought  out  the  bolometer,  which 
was  so  admirably  adapted  to  the  measurement  of  the 
minute  energy  of  radiations,  a  great  mass  of  valuable 
experimental  data  was  obtained,  bearing  on  the  spectral 
distribution  of  the  energy  of  the  radiation  emitted  by 
various  bodies.  Among  the  most  important  of  these 
contributions  must  be  mentioned  the  researches  of  Pas- 
chen,  who  examined  the  distribution  of  energy  in  the 
emission  and  absorption  spectra  of  various  substances. 
Among  the  experimental  facts  established  by  these 
researches  were,  that  by  far  the  largest  portion  of  the 
energy  in  the  spectrum  was  found  in  the  infra-red  region, 
that  the  position  of  the  wave  length  having  the  maxi- 
mum energy  depended  on  the  temperature  of  the  body, 
and  that,  as  the  temperature  was  raised,  the  energy  of  all 
the  waves  emitted  increased,  but  the  shorter  waves  more 


180 


HIGH   TEMPERATURES. 


rapidly  than  the  longer,  so  that  the  position  (wave  length) 
of  maximum  energy  in  the  spectrum  shifted  to.\ard 
shorter  wave  lengths.  These  facts  are  well  illustrated 


2650 


ENERGY  CURVES 

FOR 

BLACK.  BODY. 


//.-*-          I 


234 

FIG.  39.— Energy  Curves. 


by  the  curves  shown  in  Fig.  39,  taken  from  a  paper  by 
Lummer  and  Pringsheim,  in  which  the  ordinates  are  pro- 
portional to  the  intensity  of  radiation  emitted  by  a  black 
body,  and  the  abscissas  are  wave  lengths  (in  thousandths 


THE  LAWS  OF  RADIATION.  181 

of  a  millimeter).  Such  curves,  as  are  here  shown,  where 
the  temperature  is  constant  and  the  energy  is  meas- 
ured corresponding  to  radiations  of  different  wave  lengths 
emitted  by  a  body,  are  called  energy  curves,  i.e.,  the  relation 
determined  is  J=f(X)  for  T  =  constant,  where  J=  energy 
corresponding  to  wave  length  X,  strictly  the  energy  com- 
prised in  the  region  of  the  spectrum  between  X  and  X  +  dX, 
and  T  is  the  absolute  temperature  of  the  radiating  source. 
It  is  also  interesting  to  study  the  change  in  the  intensity 
of  some  particular  wave  length  as  the  temperature  of 
the  radiating  source  is  changed,  i.e.,  to  find  J  =  F(T)  for 
X=  constant.  This  can  of  course  be  done  by  exposing 
the  bolometer  strip  in  a  fixed  part  of  the  spectrum  and 
observing  the  galvanometer  deflections  as  the  tempera- 
ture is  changed.  The  curves  in  this  way  for  J=F(T) 
are  called  isochromatic  curves. 

Wien's  Laws.  —  Wien  was  led  from  theoretical  considera- 
tions to  state  that  "when  the  temperature  increases,  the 
wave  length  of  every  monochromatic  radiation  diminishes 
hi  such  a  way  that  the  product  of  the  temperature  and 
the  wave  length  is  a  constant/' 


Hence  for  the  wave  length  of  the  maximum  energy,  Xm, 
we  have 

XmT=  const.  =  2930  ......     (I) 

This  is  known  as  the  "  Wien  displacement  law  "  and  is 
simply  a  mathematical  statement  of  the  fact  that  as 
the  temperature  of  the  radiating  source  is  changed  the 
wave  length  having  maximum  energy  in  the  spectrum  will 
be  changed  in  such  a  way  that  the  product  of  this  wave 
length  and  the  corresponding  absolute  temperature  of 


182  HIGH   TEMPERATURES. 

the  source,  77,  is  equal  to  a  constant.  Wien  then  com- 
bined the  above  relation  with  the  Stefan-Boltzmann  law 
and  was  led  to  the  relation  that 

Em*xT~5  =  constant  =  B,     ....     (II) 

in  which  Em&K  indicates  the  energy  corresponding  to  the 
wave  length  of  the  maximum  energy  and  T  is  the  abso- 
lute temperature  of  the  radiating  source  (black  body). 
Both  of  these  generalizations  of  Wien  for  the  radiations 
emitted  by  a  black  body  have  received  the  most  con- 
vincing experimental  verification  throughout  the  widest 
ranges  of  measurable  temperatures  that  are  at  present 
available  to  the  experimentalist. 

As  an  illustration  of  the  experimental  evidence  in  sup- 
port of  these  two  laws  of  radiation,  the  following  table 
has  been  added,  taken  from  a  paper  by  Lummer  and 
Pringsheim  on  the  radiation  from  a  black  body: 


Am              Em 

Absolute 
A=XmT    B  =  EmT-*  Tempera-  3 
ture. 

-ft 

i 

'?n 

-      Diff. 

a 

'meai 

4. 

53 

2 

.026 

2814 

2190. 

10-17    621°. 

2 

621. 

3 

+  0°. 

1 

4 

.08 

4 

.28 

2950 

2166 

723 

721.5 

i 

5 

3 

.28 

13 

.66 

2980 

2208 

908 

.5 

910 

1 

+  1  • 

0 

2 

.96 

21 

.50 

2956 

2166 

998 

.5 

996 

.5 

-2  . 

0 

2 

.71 

34 

.0 

2966 

2164 

1094 

.5 

1092.3 

-2  . 

2 

2 

.35 

68 

.8 

2959 

2176 

1259 

.0 

1257 

.5 

-1   . 

5 

2 

.04 

145 

.00 

2979 

2184 

1460 

.4 

1460 

.0 

-0  . 

4 

1 

.78 

270 

.8 

2928 

2246 

1646 

1653.5 

+  7  . 

5 

Mean    2940       2188. 10~17 

As  will  be  seen,  these  results  of  experiment  are  in  most 
satisfactory  argeement  with  these  laws,  when  one  con- 
siders the  experimental  difficulties  that  are  involved 
in  the  measurements.  In  the  value  for  B  the  tempera- 


THE  LAWS  OF  RADIATION.  183 

ture  enters  to  the  5th  power,  so  that  a  small  error  in 
the  temperature  produces  a  very  marked  effect  on  the 
value  of  B.  Paschen  later  obtained  /*mr=2920. 

Wien  also  published  the  result  of  a  further  theoretical 
investigation  on  the  spectral  distribution  of  energy  in 
the  radiation  of  a  black  body,  in  which  he  was  led  to 
the  conclusion  that  the  energy  J  corresponding  to  any 
wave  length  was  represented  by 


rT 


(Ill) 


where  J  is  the  energy  corresponding  to  wave-length  X,  T  is 
the  absolute  temperature  of  the  radiating  black  body,  e  is 
the  base  of  the  natural  system  of  logarithms,  and  cv  and  c2 
are  constants. 

The  subsequent  experimental  work  of  Beckman,  Rubens, 
and  others  has  shown  that  Wien's  distribution  law  does 
not  hold  for  long  wave  lengths,  although  it  amply  suf- 
fices throughout  the  whole  visible  spectrum,  and  may 
be  applied  in  all  cases  where  ^r<3000. 

Planck  has  deduced  an  expression  analogous  to  Wien's 
which  applies  with  exactness  for  all  wave-lengths  and 
temperatures.  His  law,  which  reduces  to  Wien's  for 
small  values  of  X,  may  be  written 


Other  radiation  laws  have  also  been  suggested,  but 
Planck's  seems  to  best  satisfy  both  experiment  and 
theory. 

For  the  radiation  from  all  substances  that  have  been 


184 


HIGH   TEMPERATURES. 


examined   experimentally,   it  has   been   found   that   the 
"  displacement  law," 


i  T— const.  = 


(la) 


still  holds  true,  although  the  radiation  may  depart  far 
from  that  for  a  black  body.  In  this  case,  however,  the 
value  of  the  constant  is  different  from  that  for  a  black 
body.  Thus  for  polished  platinum  Lummer  and  Prings- 
heim  found  ^  =  2626. 

For  the  radiation  from  other  than  a  black  body  the  law 
of  maximum  energy  applies  only  in  the  modified  form 


EmT~a  =  const.  =  B1} 


(Ila) 


where  a  cannot  be  less  than  5  and  is  not  probably  ever 
greater  than  6,  the  value  found  by  Lummer  and  Prings- 
heim  for  polished  platinum.  The  general  form  of  Wien's 

_C2_ 

law  III  takes  the  form  J  =  c^~ae    w-}  where  6  >  a  >  5. 

Lummer  and  Pringsheim  found  the  following  limits  of 
temperature  as  given  by  the  Wien  relation  la: 


*m 

J^max 

^min 

Electric  arc.  .   . 

0  7  fi 

4200  abs 

3750  abs 

Nernst  lamp  

1  2 

2450 

2200 

Auer  burner.  .  . 

1  2 

2450 

2200 

Incandescent  lamp  

1  4 

2100 

1875 

Candle  

1  5 

1960 

1750 

Argand  burner  

1  55 

1900 

1700 

Lummer  and  Pringsheim  also  heated  a  carbon  tube 
electrically  to  about  2000°  C.  and  observed  the  tempera- 
ture inside  simultaneously  with  instruments  making  use 
of  the  several  radiation  laws; 


THE  LAWS  OF  RADIATION.  185 

Method.  T  absolute. 

(2310 
Photometric <  2320 

(2330 

i  2330 
Total  radiation \  2345 

(2325 

Energy  maximum \  2320 

This  complete  concordance  at  such  a  high  temperature 
between  the  different  radiation  methods  gives  further  con- 
fidence in  the  legitimacy  of  their  indefinite  extrapolation 
for  non-luminescent  bodies.  Waidner  and  Burgess  have 
also  found  that  this  accord  probably  exists  at  the  tem- 
perature of  the  electric  arc,  3600°  C. 

Applications  to  Pyrometry. — It  is  evident  that  theoret- 
ically any  of  these  laws  and  their  various  consequences 
might  be  used  as  a  basis  of  pyrometry,  but  practically  it 
is  not  convenient  to  make  use  of  all  of  them.  The  dis- 
placement law  (XmT  =  A)  and  the  maximum-energy  law 
(EmT~5  =  B)  of  Wien  are  well-established  relations,  but 
in  practice  it  is  exceedingly  difficult  to  construct  instru- 
ments of  sufficient  sensibility  to  give  any  considerable 
precision,  and  any  industrial  pyrometer  using  these  prin- 
ciples is  out  of  the  question  .at  the  present  time.  The 
reason  of  the  lack  of  sensibility  with  the  relation  XmT=A 
is  due  to  the  fact  that  the  exact  position  of  the  wave 
length  possessing  the  maximum  of  energy  is  very  difficult 
to  locate,  especially  at  relatively  low  temperatures;  see 
Fig.  39.  The  value  of  the  maximum  energy  could  perhaps 
be  measured  more  readily,  but,  as  this  quantity  varies  as 
the  fifth  power  of  the  temperature,  there  would  hardly  be 
any  preference  for  this  over  the  former  method. 

There  have  been,  however,  several  most  convenient, 
simple,  and  very  accurate  instruments  devised  which  are 


186  HIGH   TEMPERATURES. 

based  either  on  the  use  of  Stefan's  law  (E 

or  Wien's  distribution  law  \J  =  cf*>e~~w)  ,  either  directly 
or  indirectly,  and  in  the  two  following  chapters  we  shall 
treat  of  these  at  some  length. 

Crova  suggested  that  the  upper  limit  of  the  spectrum 
of  an  incandescent  body  might  be  used  as  a  measure  of 
this  temperature,  and  Hempel  has  recently  tried  this 
method  with  a  special  form  of  spectroscope,  using  a 
luminescent  screen  for  observing  when  the  upper  spectrum 
limit  is  beyond  the  visible  radiations;  but,  as  compared 
with  the  photometric  and  radiation  pyrometers,  only 
crude  results  can  be  obtained. 


CHAPTER  VIII. 
HEAT-RADIATION  PYROMETER. 

Principle. — The  quantity  of  heat  that  a 'body  receives 
by  radiation  from  another  body  depends  on  certain  condi- 
tions relative  to  each  of  the  two  bodies,  which  are: 

1.  Temperature; 

2.  Surface; 

3.  Distance  apart; 

4.  Emissive  and  absorbing  power. 

In  order  to  utilize  heat  radiation  for  the  determination 
of  temperatures,  one  measures  a  heat  change  produced  on 
the  body  used  as  an  instrument  by  the  body  to  be  studied ; 
this  heat  change  is  either  a  rise  of  temperature  or  a  re- 
sulting phenomenon,  such  as  a  change  of  electrical  resist- 
ance, thermoelectromotive  force,  etc. 

The  quantity  of  heat  given  off  is  proportional  to  the 
radiating  surface  S,  and  varies  inversely  as  the  square  of 
the  distance  I. 

a-lc8 -ifi -V'E  d* 
q_lc--lcj2-ic  £•— , 

d  being  the  diameter  of  the  radiating  surface  S,  E  its 
emissive  power. 

Now,  -j  is  the  apparent  diameter  of  the  object;  the 

quantity  of  heat  radiated  depends  then  upon  the  solid 
angle  under  which  the  object  is  seen.     Any  instrument 

1S7 


188  HIGH  TEMPERATURES. 

making  use  of  the  intensity  of  radiation  must,  therefore, 
have  a  receiving  device  of  sufficiently  small  area  so  that 
it  may  be  completely  covered  by  th  desired  radiation. 

The  emissive  power  E  is  very  variable  from  one  substance 
to  another  as  we  have  seen,  and  for  the  same  substance 
variable  with  the  temperature.  It  would  be  desirable  to 
determine  this,  but  that  is  difficult,  often  impossible, 
especially  at  high  temperatures,  although  some  advance 
has  been  made  in  this  direction  as  we  have  seen  in  the 
preceding  chapter. 

The  coefficient  ft"  is  a  function  of  the  temperature 
alone,  which  expresses  the  law  of  variation  of  the  radia- 
tion with  he  temperature.  This  law  should  be  determined 
in  the  first  place.  It  is  on  the  more  or  less  exact  knowl- 
edge of  this  law  that  the  entire  accuracy  of  the  results  de- 
pends. We  have  seen  that  Stefan's  law  (p.  177)  satisfies 
all  requirements  for  the  measurement  of  total  radiation, 
although  the  early  experimenters,  working  before  the 
establishment  of  this  law,  were  obliged  to  express  their 
results  empirically. 

Let  us  see  now  what  are  the  experimental  arrangements 
which  have  been  used  to  measure  the  intensity  of  heat 
radiation;  these  measurements  have  had  for  their  only  aim, 
until  recently,  the  determination  of  the  sun 's  temperature, 
but  they  may  serve  other  uses. 

Pouillet's  Experiments. — Before  Pouillet,  Gasparin  had 
already  made  some  trials.  His  apparatus  consisted  of  a 
hollow  brass  sphere  mounted  on  a  foot  and  blackened ;  a 
thermometer  was  used  to  measure  the  rise  in  temperature 
of  the  water  contained  in  the  sphere.  The  advantage 
of  this  arrangement  was  that  the  apparatus  was  always 
mrned  properly  toward  the  sun. 

The  pyrrheliometre  .of  Pouillet  consists  of  a  calorimeter 
which  measures  directly  the  heat  received  by  radiation 


HEAT-RADIATION  PYROMETER. 


189 


(Fig.  40) .  A  very  thin  silver  box  is  carried  by  a  hollow  tube, 
cut  along  a  generatrix  to  let  the 
thermometer  be  seen.  The  box  is 
of  100  mm.  diameter  by  15  mm. 
height;  it  contains  100  cc.  of  water. 
At  the  lower  part  of  the  box  is 
located  a  metallic  disk  of  the  same 
diameter  as  the  box,  and  serving  to 
turn  the  apparatus  toward  the  sun  ; 
it  suffices,  in  fact,  for  the  shadows 
of  the  box  and  disk  to  coincide 
exactly  in  order  that  the  system  be 
properly  pointed.  A  knob  serves  to 
turn  the  apparatus  about  its  axis 
in  order  to  stir  the  water.  Finally 
a  support  gives  the  means  of  placing 
the  system  in  any  desired  orienta- 
tion. 

To  take  an  observation,  the  ap- 
paratus is  set  up  and  shielded  from 
the  sun's  action  by  means  of  a 

screen;  the  readings  of  the  thermometer  are  taken  for 
five  minutes;  the  screen  is  removed  and  the  thermometer 
is  read  for  five  minutes ;  the  screen  is  put  back,  and  a  new 
set  of  readings  of  the  thermometer  for  five  minutes  is 
taken. 

The  first  and  the  third  sets  furnish  the  corrections  due 
to  the  surroundings.  Pouillet  observed  in  this  way  a  rise 
of  temperature  of  1°  in  five  minutes. 

In  the  determination  of  the  temperature  of  the  sun  it 
was  evidently  necessary  to  take  into  account  the  heat 
absorbed  by  the  atmosphere  (it  is  about  20  per  cent  of  the 
total  radiation  from  the  sun).  Pouillet  found  by  this 
method  1300°  for  the  temperature  of  the  sun. 


FIG.  40. 


190 


HIGH   TEMPERATURES. 


Experiments  of  Violle. — Violle  makes  use  of  an  actino- 
metre,  whose  principle  is  quite  different  from  that  of  the 
preceding  apparatus;  one  observes  the  stationary  equilib- 
rium of  a  thermometer  receiving  simultaneously  radiation 
from  an  enclosure  at  fixed  temperature,  and  that  from  the 
hot  substance  to  be  investigated  (Fig.  41). 

The  apparatus  consists  of  two  spherical  concentric 
coverings  of  brass,  in  which  a  water  circulation  may  be 
set  up  at  constant  temperature,  or  ice  may  be  substituted 
for  water.  The  inner  covering  of  150  mm.  diameter  is 
blackened  inside.  The  thermometer  has  a  spherical  bulb 
whose  diameter  varies  from  5  to  15  mm.;  the  surface  of 


FIG.  41. 

the  bulb  is  also  blackened.  The  scale  is  divided  into  fifths 
of  a  degree.  The  entrance-tube  carries  a  diaphragm 
pierced  with  holes  of  different  diameter;  on  the  extension 
of  this  tube  is  located  an  opening  closed  by  a  ground- 


HEAT-RADIATION  PYROMETER.  191 

glass  mirror  slightly  blackened,  which  permits  of  deter- 
mining that  the  solar  rays  fall  quite  exactly  upon  the  ther- 
mometer bulb. 

The  establishment  of  the  temperature  equilibrium  re- 
quires fifteen  minutes,  and  the  differences  of  temperature 
observed  vary  from  15°  to  20°. 

Yiolle  found  in  this  way,  for  the  temperature  of  the  sun, 
figures  varying  from  1500°  to  2500°. 

Pouillet  and  Violle  made  use  of  Dulong  and  Petit  's  law 
of  radiation, 

q  =  a', 

that  the  discoverers  had  established  by  observations  reach- 
ing only  to  300°. 

The  constant  a  may  be  determined  for  each  apparatus 
by  a  single  experiment  made  at  a  known  temperature. 
This  law,  as  we  shall  show  farther  on,  is  not  exact,  so  that, 
according  to  the  temperature  used  to  determine  the  con- 
stant, a  different  value  of  the  latter  is  found,  and  conse- 
quently also  different  values  at  temperatures  calculated, 
assuming  this  law  to  hold.  This  is  the  reason  for  the 
differences  between  the  three  figures,  1300,  1500,  and 
2500,  of  Pouillet  and  Violle.  They  correspond  to  deter- 
minations of  the  constant  obtained  by  means  of  prelimi- 
nary experiments  made  at  the  temperatures  of  100°,  300°, 
and  1500°. 

The  elder  Secchi,  making  use  of  Newton  's  formula, 


still  more  inexact,  found  for  the  sun's  temperature  several 
millions  of  degrees. 

Work  of  Rosetti.  —  The  Italian  scientist,  Rosetti,  was 
the  first  to  grasp  the  fundamental  importance  of  the  choice 


192 


HIGH 


of  the  law  assumed  for  radiating  power;  he  showed  that  a 
graduation  made  by  an  experiment  at  300°  gave  for  the 
temperature  of  a  body  heated  in  the  oxhydrogen  flame: 

46,000  if  one  uses  the  law  of  Newton ; 

1,100"    "     ;"     "     "    "  Dulong  and  Petit. 
Now  the  temperature  of  the  oxyhydrogen  flame  is  about 
2000°. 

This  physicist  used  a  thermoelectric  pile  whose  sensi- 
bility could  be  changed  without  touching  the  element;  in 
the  apparatus  of  Violle  it  is  necessary,  on  the  contrary,  to 
change  the  thermometer,  a  proceeding  which  renders  the 
observations  comparable  with  difficulty. 

The  pile  (Fig.  42)  consists  of  twenty-five  sheets  of 
bismuth  and  antimony;  these  sheets  are  very  thin,  for  the 
whole  of  the  apparatus  is  but  5  mm.  on  a  side.  The  whole 
is  enclosed  in  a  small  metallic  tube. 


FIG.  42. 

To  make  an  experiment  there  is  placed  before  the  pile  a 
screen  filled  with  water,  which  is  removed  at  the  instant 
of  taking  an  observation. 


HEAT-RADIATION  PYROMETER.  193 

A  preliminary  calibration  made  with  a  Leslie's  cube  of 
iron  filled  with  mercury  that  is  heated  from  0°  to  300° 
gave  the  following  results: 

Excess  of  the  Temperature  of 


32°.  8  ...................      10° 

112  .8  ....................     55 

192  .8  ...................    141  .9 

272  .8  ...................    283  .5 

Newton's  law  and  that  of  Dulong  and  Petit  giving  no 
concordance  between  the  numbers  observed  and  those 
computed,  Rosetti  proposed  the  formula 

Q  =  aT\T-6)-b(T-0), 

where  T=  absolute  temperature  of  the  radiating  body, 
0  =  the  absolute  temperature  of  the  surroundings.  This 
formula  with  two  parameters  permits  necessarily  a  closer 
following  of  the  phenomenon  than  a  formula  with  but  a 
single  parameter. 

y_0  Deflections  Deflections  Computed. 

Observed.  Dulong's  Law.        Rosetti's  Law. 

50  A=   17.2  4+2.12  A-0.23 

100  46.4  +0.95 

150  90.1  -2.12  +0.70 

200  151.7  +4.82  +0.99 

250  234.7  +2.83  -0.12 

Rosetti  showed  later  that  the  formula  he  proposed  did 
not  lead  to  absurd  results  for  higher  temperatures.  A 
mass  of  copper  was  heated  to  redness  in  a  flame,  and  the 
temperature  was  estimated  by  the  calorimetric  method 
(a  quite  uncertain  method,  as  the  variation  of  the  specific 
heat  of  copper  is  not  known).  The  two  methods  gave 


194  HIGH   TEMPERATURES. 

respectively  735°  and  760°.  This  difference  of  25°  is  less 
than  the  experimental  uncertainties. 

Disks  of  blackened  metal  placed  in  the  upper  part  of  a 
Bunsen  flame  gave,  according  to  the  formula,  temperatures 
of  the  order  of  1000°;  oxy chloride  of  magnesium  in  the 
oxyhydrogen  blast-lamp  gave  2300°.  All  these  numbers 
are  possible. 

Rosetti,  using  this  formula,  found  10,000°  for  the  tem- 
perature of  the  sun,  this  figure  resulting  from  an  extra- 
polation above  300°. 

Experiments  of  Wilson  and  Gray.  —  These  physicists 
measured  the  intensity  of  radiation  by  means  of  a  thermo- 
electric couple,  a  method  first  conceived  by  Deprez  and 
d'Arsonval.  A  movable  coil  made  of  two  different  metals 
(silver  and  palladium)  is  suspended  by  a  silk  cocoon  fibre 
between  the  poles  of  a  magnet.  The  solar  radiation  is 
allowed  to  fall  upon  one  of  the  junctions,  while  upon  the 
other  junction  is  directed  a  source  of  heat  which  exactly 
balances  the  first.  As  the  temperature  of  this  auxiliary 
source  is  necessarily  the  lesser,  it  is  necessary  that  the 
apparent  angle  which  it  subtends  at  the  galvanometer 
be  the  greater. 

Wilson  and  Gray  used  an  apparatus  similar  to  the 
radiomicrometer  of  Boys.  The  suspending  fibre  is  of 
quartz;  the  metals  employed  are  bismuth  and  antimony: 
the  electromotive  force  so  produced  is  twenty  times  greater 
than  that  obtained  with  "the  palladium-silver  couple.  The 
metallic  strips  R  and  R'  (Fig.  43)  are  very  thin  (0.1  mm.), 
which  renders  the  construction  of  the  apparatus  quite 
delicate.  In  order  to  protect  the  movable  coil  against  air- 
currents,  it  is  enclosed  in  a  metallic  case  (Fig.  44) ;  an  open 
tube  lets  pass  in  the  radiation;  diaphragms  set  inside  this 
tube  prevent  air -disturbances 

Instead  of  measuring,  as  may  be  done,  the  deflection  of 


HEAT-RADIATION  PYROMETER. 


195 


the  mobile  parts,  the  investigators  preferred  to  employ  a 
null  method  making  use  of  another  radiation,  that  from 
a  modification  of  the  meldometer  of  Jolly,  an  apparatus 
used  also  for  the  graduation  of  the  radiomicrometer.  The 


AM 


R'. 
FIG.  43. 


FIG.  44. 


meldometer  (Chapter  X)  consists  of  a  strip  of  platinum 
heated  by  an  electric  current;  the  dimensions  are  as  fol- 
lows: 102  mm.  in  length,  12  mm.  in  breadth,  and  0.01  mm. 
thick.  This  strip  they  placed  in  the  midst  of  an  enclo- 
sure surrounded  by  water.  Fastened  at  one  end,  it  is 
held  in  place  at  the  other  end  by  a  spring  and  carries  on 
this  end  a  lever  to  which  is  fixed  a  mirror  arrangement 
serving  to  optically  amplify  the  variations  in  the  length  of 


196  HIGH   TEMPERATURES. 

the  strip  resulting  from  its  heating  by  the  passage  of  the 
more  or  less  intense  current. 

The  relation  between  the  change  of  length  and  the  tem- 
perature is  determined  by  means  of  the  fusion  of  very  small 
fragments  (l/10  milligramme)  of  bodies  whose  fusing-points 
are  known.  Wilson  and  Gray  used  the  following,  which 
for  the  gold  and  palladium  are  certainly  too  low: 

Silver  chloride 452° 

Gold 1045 

Palladium 1500 

With  this  apparatus  they  apparently  verified,  up  to  the 
fusion  of  platinum,  the  law  of  radiation  given  by  Stefan, 

E=k(T'-T04). 

For  the  purpose  of  graduation,  the  meldometer  was 
removed  to  a  distance,  so  that  its  action  on  the  radio- 
micrometer  was  always  the  same,  and  it  was  assumed  that 
the  intensity  varies  as  the  inverse  square  of  the  distance.  It 
is  besides  necessary  to  know  the  emissive  power  of  platinum ; 
Wilson  and  Gray  took  as  starting-points  the  results  given 
by  previous  experiments: 

t°  Emissive  Power. 

3000 & 

600 o 

800 o 

And  by  extrapolation  they  found  1/2.9  at  the  temperature 
of  1250°,  temperature  which  balanced  the  solar  radiation, 
with  the  somewhat  large  apparent  angle  subtended  by  the 
meldometer.  In  admitting,  then,  with  Rosetti  and  Young, 
a  zenith  absorption  of  30  per  cent,  the  temperature  of  the 


HEAT-RADIATION  PYROMETER.  197 

sun,  supposed  to  be  a  black  body,  was  found  equal  to  about 
6200°. 

This  figure  must  be  considerably  uncertain,  on  account 
of  the  errors  involved  in  the  fusing-points  employed  for 
graduation,  and  because  of  the  fact  that  the  radiation 
from  platinum  does  not  obey  Stefan's  law.  Furthermore 
the  constants  for  platinum  were  found  in  terms  of  those 
of  copper  oxide,  a  substance  they  found,  incorrectly,  to 
depart  more  from  a  black  body  than  polished  platinum.  ' 

Langley  and  Abbot's  Experiments. — Langley  has  de- 
vised, under  the  name  of  bolometer,  a  radiometric  appa- 
ratus which  he  has  used  only  incidentally  to  measure 
temperatures,  but  which  may  be  so  used  and  has  the 
advantage  over  the  preceding  methods  of  being  more  sen- 
sitive. 

It  consists  of  a  Wheatstone  bridge,  one  arm  of  which  is 
made  of  flat  wires  extremely  thin  (0.01  mm.)  and  very 
short  (a  few  millimeters  at  the  most).  The  variations 
of  resistance  of  this  arm  of  the  bridge  submitted  to  the 
radiation  are  measured.  The  current  passing  through 
the  system  is  capable  of  raising  its  temperature  3°  or  4°; 
the  excess  of  heat  furnished  to  one  of  the  arms  produces 
a  deflection  of  the  galvanometer. 

The  system  is  fixed  at  the  bottom  of  a  tube  which  may 
be  pointed  like  a  telescope  toward  the  body  whose  radia- 
tion is  to  be  measured;  diaphragms  fixed  at  various  points 
stop  interior  currents  of  air.  One  may  also,  by  aid  of  a 
lens,  concentrate  the  radiation  upon  the  wire  and  amplify 
very  much  in  this  way  the  effect  produced  wThen  the 
apparent  angle  of  the  object  is  small. 

The  bolometer  of  Langley  has  up  to  the  present  been 
used  almost  exclusively  to  study  the  distribution  of  radi- 
ant energy  in  the  solar  spectrum,  and  especially  in  the 
infra-red.  It  is  sufficiently  sensitive  in  the  hands  of 


198  HIGH   TEMPERATURES. 

Langley  and  Abbot  to  detect  changes  of  less  than 
0°.000001  C. 

Conditions  of  Use.  —  We  have  dwelt  at  length  upon  those 
radiation-pyrometers  which  have  been  used  up  to  the 
present  only  for  a  single  purpose,  the  estimation  of  the 
sun's  temperature,  because  it  is  possible  that  some  day  or 
other  their  usage  may  penetrate  into  industrial  works, 
where  they  may  be  of  real  service.  In  a  certain  number  of 
industrial  operations  the  temperatures  are  so  high  that  no 
substance,  not  even  platinum,  can  resist  for  long  their 
action.  When  it  is  desired  to  have  apparatus  of  con- 
tinuous indications,  and  at  the  same  time  unalterable,  it 
will  be  necessary  to  make  use  of  radiation-pyrometers. 

A  tube  of  fire-clay  passing  through  the  lining  of  the 
furnace,  and  penetrating  into  the  midst  of  the  latter  for  a 
distance  of  0.50  m.  to  1.00  m.,  closed  at  the  inner  end  and 
open  at  the  outer,  would  give  a  radiating  surface  at  the 
temperature  of  the  furnace  which  could  be  examined  by 
means  of  a  lens  projecting  upon  the  measuring  apparatus 
the  image  of  the  sealed  base  of  this  tube.  This  arrange- 
ment also  gives  radiation  obeying  very  nearly  the  laws 
we  have  discussed,  that  is,  a  black  body  is  realized  ap- 
proximately and  Stefan's  and  Wien's  laws  may  be  used 
with  radiation  instruments. 

Fery  Thermoelectric  Telescope.  —  This  pyrometer  is  the 
only  convenient  form  of  instrument  making  use  of  total 
radiation  and  based  on  Stefan's  law  (p.  177)  which  has 
come  into  practical  use  for  temperature-measurements. 
As  in  the  case  of  the  photometric  pyrometers,  the  limita- 
tions as  to  the  realization  of  a  black  body  apply  here  also. 

Use  is  made  of  the  Stefan-Boltzmann  law, 


in  the  following  way:    Radiation  from  an  incandescent 


HEAT-RADIATION  PYEOMETER.  199 

body  is  focussed  upon  a  very  sensitive  thermocouple 
and  raises  its  temperature.  The  electromotive  force  thus 
generated  at  the  junction  actuates  a  sensitive  potential 
galvanometer  in  series  with  the  couple  in  exactly  the  same 
way  as  in  the  Le  Chatelier  thermoelectric  pyrometer;  so 
that  we  have  here  a  radiation-pyrometer  which  is  direct- 
reading  by  means  of  a  pointer  on  a  scale,  and  may  there- 
fore readily  be  made  a  recording  instrument. 

The  difficulty  in  construction  of  such  an  instrument  is 
realizing  a  material  for  lens  which  is  transparent  for  all 
radiations  visible  and  invisible,  so  that  the  pyrometer 
may  be  calibrated  directly  in  terms  of  Stefan's  law  and 
so  that  its  indications  will  be  reliable  at  temperatures 
however  high.  This  is  effected  by  use  of  a  fluorite  lens 
which  for  temperatures  above  900°  C.  satisfies  the  con- 
ditions of  not  altering  appreciably  the  radiations  trans- 
mitted through  it ;  that  is  to  say,  the  ratio  of  the  radiations 
absorbed  to  the  radiation  transmitted  is  constant. 

At  low  temperatures  a  large  proportion  of  the  energy 
exists  in  the  form  of  long  wave  lengths,  and  as  fluorite  has 
an  absorption-band  in  the  infra-red  (near  6//),  it  will  absorb 
a  considerable  proportion  of  the  radiation,  and  therefore 
Stefan's  law  can  no  longer  be  assumed. 

Fig.  45  illustrates  the  construction  of  the  instrument, 
where  F  is  the  fluorite  lens,  P.  a  rack  and  pinion  for  focus- 
sing the  radiations  upon  the  thermo-junction  of  iron-con- 
stantan,  and  protected  from  extraneous  rays  by  the  screens 
C,  D,  shown  also  in  section  at  AB.  The  thermo-junction 
is  of  exceedingly  small  dimensions,  only  a  few  thousandths 
of  a  millimeter  wide,  and  is  soldered  to  a  silver  disk.  The 
leads  are  brought  out  to  the  insulated  binding-posts  b,  b' , 
so  placed  as  to  reduce  the  chances  of  extraneous  thermal 
currents  to  a  minimum.  The  circuit  is  completed  through 
a  sensitive  galvanometer  provided  with  a  scale.  A  dia- 


200 


HIGH  TEMPERATURES. 


HEAT-RADIATION  PYROMETER.  201 

phragm  fixed  in  size  and  position,  EE,  gives  an  opening 
of  constant  angle  independent  of  the  focussing  whereby 
the  cone  of  rays  striking  the  junction  is  not  changed  hi 
size  by  focussing. 

In  making  a  temperature-measurement  it  is  necessary 
to  sharply  focus  the  image  of  the  incandescent  object 
upon  the  thermo-j  unction  by  means  of  the  eye-piece  0, 
and  care  must  be  taken  that  this  image  is  of  greater  size 
than  the  junction.  This  adjustment  once  made,  the 
pyrometer  functions  indefinitely  while  sighted  upon  the 
same  object,  and  readings  of  the  galvanometer  scale  give 
temperatures  directly  from  the  calibration. 

The  precision  attainable  with  this  form  of  instrument, 
over  the  range  it  may  be  controlled  with  the  thermoelectric 
pyrometer,  is  shown  from  data  obtained  by  Fery,  assum- 
ing Stefan's  law  to  hold  in  the  form, 


where  E  is  the  total  energy  of  radiation  and  d  the  gal- 
vanometer deflection  and  T  the  absolute  temperature. 


,                  Temp,  from 
Thermocouple. 

Temp,  from 
Stefan's  Law. 

J  in 
Degrees. 

Error 
in  %. 

11 

844° 

860° 

+  16° 

1.85 

14 

914 

925 

+  11 

*.84 

17.7 

990 

990 

0 

.0 

21.5 

1054 

1060 

+  6 

.60 

26.0 

1120 

1120 

0 

.0 

32.2 

1192 

1190 

-  2 

.17 

38.7 

1260 

-10 

.80 

45.7 

1328 

-  8 

.60 

52.5 

1385 

-  5 

.36 

62.2 

1458 

1450 

-  8 

.50 

It  is  evident,  furthermore,  that  if  the  galvanometer  has 
a  uniformly  graduated  scale  and  the  temperature  Tl  cor- 
responding to  any  one  scale  reading  ^  is  known,  that  for 


202  HIGH   TEMPERATURES. 

any  other  reading  R2  may  be  found  from  the  relation 


which  also  shows  that  errors  in  the  galvanometer  readings 
are  divided  by  four  when  reduced  to  temperatures.  For 
very  high  temperatures  deflections  off  the  scale  of  the 
galvanometer  will  be  obtained.  Fery  overcomes  this  diffi- 
culty by  substituting  a  smaller  diaphragm  before  the 
objective  when  the  radiation  is  reduced  in  the  ratio  of 
the  areas  of  the  apertures.  Shunting  the  galvanometer 
will  also  accomplish  the  same  end,  and  this  latter  method 
is  probably  capable  of  more  accuracy  than  Fery's. 

The  highest  temperatures  which  may  be  estimated  by 
this  pyrometer  are  limited  only  by  the  applications  of 
Stefan's  law  to  this  extreme  region,  and  whether  Stefan's 
law  applies,  or  not,  consistent  results,  nevertheless,  will  be 
obtained. 

The  laboratory  form  of  apparatus  described  above  is 
not  suitable  for  use  in  technical  practice,  and  fluorite  is 
difficult  to  get  of  sufficient  size.  An  industrial  pyrom- 
eter is  readily  made  by  substituting  for  the  fluorite  lens 
one  of  glass,  and  for  the  delicate  galvanometer  one  of  the 
same  type  and  sensibility  as  used  in  thermoelectric  work; 
the  resulting  instrument  is  robust  and  sufficiently  sen- 
sitive for  all  practical  uses  and  as  made  has  a  range  of 
from  800°  C.  to  1600°  C.,  although  the  upper  limit  could 
readily  be  extended  by  having  two  scales  on  the  instru- 
ment, with  a  shunt. 

The  indications  of  the  industrial  form  of  this  pyrom- 
eter will  not  obey  Stefan's  law,  but  the  instrument  may 
readily  be  calibrated  by  direct  comparison  either  with  a 
thermocouple  or  with  a  laboratory  form  of  Fery  instru- 


HEAT-RADIATION  PYROMETER.  203 

ment,  and  the  scale  of  temperatures  engraved  on  the 
instrument. 

Both  types  of  instrument  can  be  use,d  to  reach  lower 
temperatures  (650°)  by  means  of  more  sensitive  galvanom- 
eters. 

Lower  temperatures  might  also  be  reached  by  converting 
the  instrument  into  a  reflecting  telescope  with  a  concave 
mirror  behind  the  thermo-junction,  and  Fery  has  just  de- 
signed such  an  instrument  with  which  temperatures  nearly 
as  low  as  600°  C.  may  be  reached. 


CHAPTER  IX. 
OPTICAL  PYROMETER. 

Principle. — Instead  of  using  the  totality  of  the  radiant 
energy  as  in  the  methods  described  in  the  preceding 
chapter,  use  is  made  of  the  luminous  radiations  only.  This 
utilization  may  be  effected  in  many  different  ways,  which 
give  methods  of  unequal  precision  and  varying  in  facility 
of  manipulation. 

Before  beginning  their  study,  it  is  well  to  recall  certain 
properties  of  radiations. 

Kirchoff's  Law. — An  incandescent  body  emits  radiations 
of  different  wave  lengths.  For  a  given  wave  length  and  a 
given  temperature  the  intensity  of  this  emitted  radiation 
is  not  the  same  for  different  bodies:  this  is  expressed  by 
saying  that  they  have  for  this  radiation  different  emissive 
powers.  Similarly,  a  body  which  receives  radiations  of  a 
given  wave  length  absorbs  a  part  of  them  and  sends  back 
another  part  by  diffusion  or  reflection;  a  certain  quantity 
may  also  traverse  the  body.  The  diffusing,  reflecting,  or 
transmitting  power  at  a  given  temperature,  for  a  given 
wave  length,  varies  from  one  body  to  another.  The  emis- 
sive power  and  the  diffusive  power  (in  the  case  of  an  opaque 
and  non-reflecting  body)  vary  always  inversely,  resting  com- 
plementary to  each  other. 

Substances  of  great  emissive  power,  as  lampblack,  have 
a  small  diffusive  power;  substances  of  small  emissive 

204 


Of    THC 

UNIVERSITY 

OPTICAL  PYROMETER.  205 

power,  as  polished  silver,  magnesia,  have  a  very  great 
diffusing  or  reflecting  power. 

If  we  take  as  the  measure  of  the  emissive  power  the 
ratio  of  the  intensity  of  the  radiation  of  the  body  consid- 
ered to  that  of  a  black  body  (p.  173)  at  the  same  tempera- 
ture, and  as  measure  of  the  diffusive  power  the  ratio  of 
the  intensity  of  the  radiation  diffused  to  the  incident 
radiation,  the  sum  of  these  two  quantities  is  equal  to 
unity. 

The  emissive  power  of  a  body  varies  from  one  radiation 
to  another,  and  consequently  also  its  diffusing  and  trans- 
mitting powers,  since  these  two  powers  are  complementary 
to  each  other.  It  follows  that  the  relative  proportions  of 
the  visible  radiations  received  or  given  off  by  a  body  are 
not  the  same;  so  that  different  bodies,  at  the  same  tem- 
perature, appear  to  us  to  be  differently  colored. 

At  the  same  temperature,  the  color  proper  to  a  body,  and 
its  apparent  color  when  it  is  lighted  by  white  light,  are 
complementary  to  each  other.  Yellow  substances,  as 
oxide  of  zinc  heated,  emit  a  greenish-blue  light.  At  tem- 
peratures less  than  2000°  the  red  radiations  predominate 
greatly  and  mask  the  inequalities  of  the  radiations  of 
other  wave  lengths.  To  render  easily  visible  the  colora- 
tions of  radiating  bodies  it  is  necessary  to  compare  them 
with  those  of  a  black  body  under  the  same  temperature 
conditions.  A  hole  pierced  in  the  body,  or  a  crack  across 
the  surface,  gives  a  very  good  term  of  comparison  to  judge 
of  this  coloration.  \ 

The  intensity  of  the  radiations  emitted  by  a  black  body 
increases  always  with  the  temperature,  and  the  more 
rapidly  as  we  approach  the  blue  region  of  the  spectrum; 
but  on  the  other  hand  the  radiations  from  the  red  end  are 
the  first  to  commence  to  have  an  intensity  appreciable  to 
vision,  so  that  the  color  of  bodies  heated  to  higher  and 


206  HIGH 

higher  temperatures  starts  with  red,  tending  towards  white 
passing  through  orange  and  yellow.  White  is,  in  fact,  the 
color  proper  to  bodies  extremely  hot,  as  is  the  sun. 

Bodies  not  black  have  a  law  of  increase  different  from 
that  for  black  bodies,  because  the  emissive  power  varies 
with  the  temperature.  It  increases  unequally  for  the 
various  radiations,  so  that  the  color  of  bodies,  with  respect 
to  the  color  of  a  black  body,  changes  with  the  temperature. 

The  following  table  gives  for  different  colors  the  ratios 
of  the  values  of  emissive  powers  of  some  bodies  to  that  of 
a  black  body.  The  red  radiation  was  observed  through  a 
glass  containing  copper,  the  green  by  aid  of  a  chromium 
copper  glass,  the  blue  through  an  ammoniacal  solution  of 
cupric  hydrate.  The  substance  covered  the  junction  of  a 
thermoelectric  couple,  and  was  cut  by  grooves;  and  it  was 
the  brightness  of  the  bottom  of  these  grooves  which  was 
compared  to  that  of  the  surface. 


Red. 

Green. 

Blue, 

<at 

1300°  ' 

0.10 

0.15 

0.20 

I 

1550 

.30 

.35 

.40 

\ 

1200 

.05 

.10 

.10 

\ 

1700 

.60 

.40 

.60 

Oxide  of  chromium 

-\ 

1200 
1700 

1.00 
1.00 

1.00 
.40 

1.00 
.30 

Oxide  of  thorium  . 

-{ 

1200 
1760 

.50 
.60 

.50 
.50 

.70 
.35 

Oxide  of  cerium.  .  . 

-{ 

1200 

.80 

1.00 

1.00 

Auer  mixture  .... 

-\ 

1200 
1700 

.25 

.40 

1.00 

The  estimation  of  temperature,  from  measurements  of 
luminous  radiations,  may,  at  least  in  theory,  be  made 
directly  in  three  different  ways,  by  utilizing: 

The  total  intensity  of  the  luminous  radiation; 


OPTICAL  PYROMETER.  207 

The  intensity  of  a  radiation  of  definite  wave  length; 

The  relative  intensity  of  radiations  of  definite  wave 
lengths. 

In  the  chapter  (VII)  on  the  laws  of  radiation  we  have 
discussed  the  recent  theoretical  and  experimental  advances 
underlying  these  methods. 

Measurement  of  the  Total  Intensity  of  Radiation. — The 
brightness  of  substances  increases  very  rapidly  with  the 
temperature.  One  may  with  the  unaided  eye  estimate  com- 
paratively this  brightness,  but  this  measurement  is  very 
uncertain,  for  lack  of  a  constant  standard  of  comparison. 
The  sensitiveness  of  the  eye  varies,  in  fact,  with  the  indi- 
vidual, with  the  light  which  the  eye  received  immediately 
preceding,  and  with  the  attendant  fatigue.  Photometric 
processes,  precise  for  comparison  with  a  standard  source, 
cannot  be  employed  on  account  of  the  change  of  hue  with 
the  temperature. 

The  following  method  might  be  tried:  trace  on  a  white 
surface,  diffusive  or  translucent  marks,  of  definite  intensity 
and  dimensions,  and  seek  what  fraction  of  the  light  must 
be  employed  to  render  the  marks  invisible.  The  indi- 
cations will  be  still  quite  variable  and  will  depend  upon 
the  degree  of  the  eye's  fatigue. 

We  can  then  say  that  there  actually  exists  no  definite 
method  based  on  the  appreciation  of  the  total  intensity  of 
luminous  radiation  for  the  estimation  of  'temperatures. 

Measurement  of  the  Intensity  of  a  Simple  Radiation. — 
We  may  estimate  the  temperature  of  a  body  from  the 
intensity  of 'one  of  its  radiations,  provided  that  we  know 
the  emissive  power  of  the  body  at  that  temperature  and  the 
law  of  variation  of  this  radiation  determined  in  terms  of 
the  air-thermometer. 

The  emissive  power  varies  with  the  temperature,  and 
generally  is  not  known.  It  might  seem  that  this  would 


208  HIGH  TEMPERATURES. 

be  enough  to  reject  this  method  and  similar  methods 
by  radiation.  But  this  is  not  so,  for  the  following 
reasons  : 

1.  At   temperatures    higher    than    the    fusing-point   of 
platinum  there  is  no  other  pyrometric  method  at  present 
applicable. 

2.  A  great  many  bodies  have  a  considerable  emissive 
power,  nearly  unity,  and  particularly  some  bodies  of  indus- 
trial importance,  as  iron  and  coal. 

3.  The  variation  of  radiation  with  temperature  is  suffi- 
ciently marked  so  that  the  errors  committed  in  neglecting 
the  emissive  power  are  small.     Thus  at   1000°  the  red 
radiation  emitted  by  carbon  is  quadrupled  for  an  interval 
of  100°;   it  is  doubled  at  1500°  for  the  same  temperature 
interval. 

Then,  except  for  some  bodies  exceptionally  white,  the 
emissive  powers  at  high  temperatures  are  superior  to  0.5. 
By  taking  them  equal  to  0.75,  the  greatest  error  that  will 
be  made  for  the  ordinary  temperatures  comprised  between 
1000°  and  1500°  will  be  from  25°  to  50°. 

Furthermore,  in  cases  where  the  emissive  power  is 
unknown,  a*n  optical  pyrometer  will  still  give  a  consistent 
temperature  scale  for  a  give^body,  i.e.,  in  terms  of  black- 
body  temperatures  (p.  176). 

Optical  Pyrometer  of  Le  Chatelier. — Ed.  Becquerel  had 
proposed  in  1864  to  refer  the  measurement  of  high  tem- 
peratures to  the  measurement  of  the  intensity  of  red 
radiations  emitted  by  incandescent  bodies ;  but  this  method 
had  never  been  realized  in  a  complete  manner,  and  still  less 
employed.  Le  Chatelier,  taking  up  the  question,  devised 
an  experimental  arrangement  suitable  for  such  measure- 
ments, and  he  determined  a  law  of  radiation  of  substances 
in  terms  of  the  temperature. 

Photometer.  —  For    these  measurements  a    photometric 


OPTICAL  PYROMETER. 


209 


apparatus  is  required  which  gives,  not  as  do  the  ordinary 
photometers,  a  measurement  of  the  total  illumination  pro- 


CO 


duced  by  a  source  (illumination  which  varies  with  the 
dimensions  of  this  source),  but  the  intrinsic  brightness  of 


210  HIGH   TEMPERATURES. 

each  unit  of  surface.  Use  may  be  made  of  a  photometer 
based  on  a  principle  due  to  Cornu. 

The  apparatus  (Figs.  46  and  47)  consists  essentially  of 
a  telescope  which  carries  a  small  comparison-lamp  at- 
tached laterally.  The  image  of  the  flame  of  this  lamp  is 
projected  on  a  mirror  M  at  45°  placed  at  the  principal  focus 
of  the  telescope.  One  adjusts  for  equality  of  intensity  the 
images  of  the  object  that  is  viewed  and  of  the  comparison- 
flame,  these  images  being  side  by  side. 

The  teLscope  comprises  an  objective  in  front  of  which 
is  placed  a  cat's-eye  diaphragm  which  admits  of  varying 
the  effective  aperture  of  this  objective,  and,  beyond,  a  stand 
destined  to  carry  tinted  absorbing-glasses. 

At  the  focus  of  the  objective  is  a  mirror  inclined  at  45° 
which  reflects  the  image  of  the  lamp  projected  by  an 
intermediary  lens.  An  ocular,  before  which  is  placed  in  a 
set  position  a  monochromatic  glass,  serves  for  observing 
the  images  of  the  flame  and  of  the  object. 

To  the  lamp  is  fixed  a  rectangular  diaphragm  which 
stops  the  luminous  rays  not  utilized  and  which  carries  a 
stand  to  receive  tinted  absorbing-glasses. 

The  edge  of  the  mirror  at  45°  is  in  the  plane  of  the 
image  of  the  source  studied,  so  that  the  reflected  image 
and  the  direct  image  are  side  by  side,  separated  only  by  the 
edge  of  the  mirror.  This  mirror,  according  to  a  method 
devised  by  Cornu,  is  made  of  a  plate  of  black  glass  cut  with 
a  diamond,  which  gives  a  very  sharp  edge. 

In  order  to  vary  the  relative  intensities  of  the  images, 
one  thus  employs  simultaneously  tinted  glasses  placed 
before  one  or  the  other  of  the  two  objectives,  and  the 
cat's-eye  mentioned.  A  screw  allows  of  varying  the  aper- 
ture of  this  cat's-eye,  and  a  suitable  scales  indicates  the 
dimensions  of  this  opening. 

It  is  very  important  that  the  tinted  glasses  have  an 


OPTICAL  PYROMETER. 


211 


absorbing  power  as  uniform  as  possible  and  do  not  possess 
absorption-bands.  These  conditions  are  fulfilled  by  cer- 
tain smoked  glasses  of  ancient  make  (CuO,Fe203;MnO2) ; 
for  the  fabrication  of  these  glasses  use  is  now  made  of 
the  oxides  of  nickel  and  cobalt,  which  give  absorption- 
bands. 

To  determine  the  absorbing  power  of  these  glasses,  a 
measurement  is  made  with  and  without  them;   the  ratio 


FIG.  47. 

of  the  squares  of  the  aperture  of  the  cat's-eye  gives  the 
absorbing  power. 

For  monochromatic  screens  one  may  use: 
1.  Red  copper  glass,  which  lets  pass  ^=659,*  about. 
This  one  is  preferable,  as  it  is  more  nearly  monochromatic 
and  because  measurements  at  low  temperatures  may  be 
made  with  it,  the  first  radiations  emitted  being  red. 

*  Red  glasses  furnished    by  the  maker  Pellin,  Paris,  have  an 
equivalent  wave  length  of  about  A=632. 


212  HIGH   TEMPERATURES. 

2.  Green  glass  (^  =  546,  about).     The  observations  are 
then  easier  than  in  the  red  for  some  eyes,  but  they  can  be 
commenced  only  at  higher  temperatures. 

3.  Ammoniacal  solution  of  copper  oxide  (^  =  460,  about). 
The  use  of  this  last  screen,  which  is  far  from  monochro- 
matic, is  without  interest;  the  eye  is  only  slightly  sensi- 
tive to  the  blue  radiations,  and  these  last  become  some- 
what intense  only  at  high  temperatures. 

Adjustment  of  the  Apparatus. — There  are  in  the  appa- 
ratus two  parts  which  require  very  careful  adjustment  for 
best  results,  and  these  parts  should  consequently  be  so 
made  as  to  admit  of  the  necessary  manipulation  to  obtain 
the  desired  effect. 

1.  The  luminous  beam  coming  from  the  lamp  and  which 
is  reflected  by  the  mirror,  and  that  which  comes  directly 
from  the  object  viewed,  should  penetrate  into  the  eye  in 
their  totality.  This  condition  is  fulfilled  if  the  images 
of  the  two  objectives  given  by  the  ocular  are  super- 
posed. 

This  is  verified  by  examining  with  a  lens  these  two 
images  which  are  formed  slightly  behind  the  collar  of  the 
ocular.  It  is  evidently  necessary,  in  order  to  see  them,  to 
illumine  the  two  objectives,  one  with  the  lamp,  the  other 
with  any  source  of  light.  If  the  superposition  does  not 
exist,  it  is  established  by  trial  by  turning  the  screws  which 
hold  the  mirror.  If  it  is  not  too  severely  jarred,  the  appa- 
ratus should  remain  indefinitely  in  adjustment. 

In  order  that  a  steady  light  may  be  had,  certain  pre- 
cautions in  the  adjustment  of  the  comparison-lamp  are 
necessary.  As  far  as  possible,  one  should  always  employ 
the  same  gasolene.  The  flame  should  have  a  constant 
height,  equal,  for  example,  to  the  window  of  the  rectangular 
diaphragm  placed  before  the  flame.  Its  image  should  be 
cut  exactly  in  two  by  the  edge  of  the  mirror;  a  result 


OPTICAL  PYROMETER. 


213 


obtained    by    turning    the   lamp   in   its   stand,  which  is 
eccentric  (Fig.  48). 

Finally,  before  taking  an  observation, 
one  must  wait  some  ten  minutes  for  the 
lamp  to  come  into  heat  equilibrium; 
then  only  does  the  flame  possess  a  con- 
stant brightness. 

Measurements. — In  order  to  take  an 
observation,  a  body  selected  as  stand- 
ard, as  the  flame  of  a  stearine  can- 
dle or  the  flame  of  a  kerosene  lamp, 
is  examined ;  one  observes : 

1.  n0,    the    number    of    absorbing- 
glasses  ; 

2.  d0,  the  aperture  of  the  cat's-eye; 

3.  /0,  the  extension  of  the  objective 
for  focussing. 

The  same  process  is  followed  for 
the  source  to  be  studied,  and  the 
numbers  nl}  dlf  ^  are  found.  FIG.  48. 

k  being  the  absorption  coefficient  of  the  tinted  glasses, 
we  have: 


/m 

i    W 


j-  „ 


For  the  glasses  mentioned,  the  absorption  coefficients 
are: 

k = Vn ,  corresponding  to  yl  =  659  ; 

fr=Y7,  "  "  A=546; 

If  —  */  "  {t  3 

"          /  10J  A 


For  very  small  objects  which  would  have  to  be  placed 
very  near,  a  supplementary  objective  is  put  in  front  of  the 
telescope;  the  object  is  placed  in  the  principal  focus  of  this 


214  HIGH    TEMPERATURES. 

new  lens,  the  objective  of  the  apparatus  being  focussed  for 
parallel  rays.  The  absorptive  power  of  this  supplementary 
lens  is  reckoned  as  Y10. 

Details  of  an  Observation. — The  first  operation  to  make 
is  the  determination  of  the  absorption  coefficients  of  the 
absorbing-glasses.  For  that,  one  views  an  object  of  suit- 
able brightness  once  with  the  tinted  glass  before  the  cat's- 
eye  and  then  without  this  glass.  Let  N  be  the  aperture 
of  the  cat's-eye  without  tinted  glass,  and  N'  the  aperture 
with  such  a  glass.  The  coefficient  k  of  absorption  is 


The  following  observations  furnish  data  for  the  deter- 
mination of  the  absorbing  powers  of  different  glasses 
employed  in  the  course  of  studies  relative  to  the  radiations 
from  incandescent  mantles. 

Emissive  Power.  —  Before  being  able  to  establish  the 
relation  which  exists  between  the  intensity  of  radiation  of 
incandescent  bodies  and  their  temperature,  it  is  necessary 
to  know  the  emissive  powers  of  these  bodies.  For  this 
measurement  use  is  made  of  the  principle  stated  above, 
that  the  interior  of  fissures  in  bodies  may  be  considered  as 
enclosed  in  an  envelope  at  uniform  temperature.  The 
emissive  power  is  thus,  at  the  temperature  considered, 
equal  to  the  ratio  of  the  luminous  intensity  of  the  surface 
to  that  of  the  bottom  of  deep  fissures,  with  the  condition, 
evidently,  that  the  aperture  of  the  fissures  be  sufficiently 
small. 

The  body  to  be  studied  was  placed  in  the  state  of  a  paste, 
as  dry  as  possible,  on  the  end  of  a  couple  previously 
flattened  so  as  to  take  the  form  of  a  disk  of  2  or  3  mm. 
diameter.  The  drying  was  very  slow,  so  as  not  to  have 


OPTICAL  PYROMETER. 


215 


ABSORBING-GLASS     PLACED     BEFORE    THE    SOURCE    TO     BE    STUDIED. 


Temperature. 

Aperture  of  Cat's-eye. 

Red. 

Green. 

Blue. 

1270°  (  +  1  glass)  

19.5 
5.5 

21.2 
7.9 

35 
11.1 

1270   (no  glass)  

&r=12.5 

£,,=7.2 

fc&=9.9 

ABSORBING-GLASS  PLACED  BEFORE  THE  STANDARD  LAMP. 


1  170  (no  glass)  

9  4 

16  1 

31  5 

&r=10.5 

kg=7.3 

*6=9.5 

any  swelling  of  the  mass,  and  one  obtained  in  this  way  a 
coating  possessing  fissures;  the  conditions  described  above 
are  then  satisfied.  The  end  of  the  couple  thus  prepared 
is  heated  either  in  a  Bunsen  flame  or  a  blast-lamp,  and  the 
temperature  of  the  junction  is  noted,  while,  simultaneously, 
readings  are  taken  with  the  optical  pyrometer.  In  order 
to  obtain  a  temperature  as  constant  as  possible,  it  is 
necessary  to  guard  against  currents  of  air  and  use  a  flame 
of  small  size. 
Here  are  some  results  obtained: 


I.    COUPLE     COVERED    WITH    A    MIXTURE     CONTAINING    99    PARTS    OF 
THORIUM   AND    1    OF   CERIUM. 


Temperatures.                         ^  j  ^  ^^'  ^ 

Green. 

(1)         (2) 

Blue. 
(1)         (2) 

950°  (-Igfc 

iss)  16. 

0 

. 

21 

.0 

14. 

0 

23. 

0 

1170   

15 

.5 

9. 

0 

11 

.0 

9 

.0 

12 

.0 

12.0 

1375  

7. 

0 

3. 

o 

4 

.5 

3 

2 

3 

.5 

3.5 

1525   . 

3 

.2 

2. 

0 

2 

.0 

2 

.0 

1 

.0 

1.9 

1650    (  +  1  glass) 8.3      6.0         5.0     ....         4.0 


216  HIGH  TEMPERATURES. 

II.    MAGNESIA. 

1340°  (-1  glass) 12.2      4.0        18.5       6.7       19.0       9.0 

1460    (-1  glass) 4.9      2.5          8.2       3.1         7.7       4.1 

1540    (-1  glass) 2.4      1.3         3.1       1.8        3.2      2.1 

The  numbers  give  the  divisions  of  the  cat's-eye;  those 
of  column  (1)  refer  to  the  surface,  and  those  of  column  (2) 
to  the  bottom  of  the  fissures.  The  indications  (  —  1  glass) 
and  (  +  1  glass)  mean  that  the  absorbing-glass  is  placed 
either  before  the  standard  lamp  or  before  the  source 
studied.  A  more  exact  determination  of  the  above  quan- 
tities might  be  made  with  the  electrically  treated  black 
body  (p.  174). 

Measurements  of  Intensity. — The  following  table  gives 
an  idea  of  the  order  of  magnitude  of  the  intensities  of 
different  luminous  sources,  the  measurements  of  brightness 
being  made  in  the  red.  Unity  is  the  brightness  of  the 
axial  portion  of  stearine-candle  flame. 

Carbon  beginning  to  glow  (600°) 0.0001 

Silver  melting  (950°) 0.015 

Stearine  candle,  \ 

Gas-flame,  > 1.0 

Acetate  of  amyl  lamp,    ) 

Pigeon-lamp,  with  mineral  oil 1.1 

Argand  burner,  with  chimney 1.9 

Auer  burner 2.05 

Fe3O  melting  (1350°) 2.25 

Palladium  melting 4.8 

Platinum  melting 15. 0 

Incandescent  lamp 40 

Crater  of  electric  arc 10,000 

Sun  at  midday 90,000 

Graduation. — Le  Chatelier  made  a  first  graduation  of 
his  optical  pyrometer  by  measuring  the  brightness  of  iron 


OPTICAL  PYROMETER.  217 

oxide  heated  on  the  junction  of  a  thermoelectric  couple, 
and  admitting  that,  for  the  red,  the  emissive  power  of  this 
substance  is  equal  to  unity.*  He  found  a  law  of  variation 
of  the  intensity  of  the  red  radiations  as  function  of  the 
temperature,  which  is  well  represented  by  the  formula 

3210 


in  which  unit  intensity  corresponds  to  the  most  brilliant 
axial  region  of  the  flame  of  a  candle.  (T  is  absolute  tem- 
perature.) 

The  table  below  gives,  for  intervals  of  100°,  the  intensi- 
ties of  red  radiations  emitted  by  bodies  of  an  emissive 
power  equal  to  unity.  These  numbers  were  calculated  by 
means  of  the  interpolation  formula  give  above. 

Intensities.       Temperatures.  Intensities.       Temperatures. 

0.00008  ____  600°  39  .....  1800° 

.00073  ____  700  60  .....  1900 

.0046  .....  800  93  .....  2000 

.020  ......  900  1,800  .....  3000 

.078  ......  1000  9,700  .....  4000 

.24  .......  1100  28,000  .....  5000 

.64  .......  1200  56,000  .....  6000 

1.63  .......  1300  100,000  .....  7000 

3.35  .......  1400  150,000  .....  8000 

6.7  ........  1500  224,000  .....  9000 

12.9  ........  1600  305,000  .....  10000 

22.4  ........  1700 

These  results  are  represented  graphically  in  Fig.  49. 
After  having  determined  the  value  of  the  diaphragm 

*  It  has  since  been  shown  that  the  emissive  power  of  iron  oxide 
is  less  than  unity  (see  p.  178),  but  this  fact  does  not  materially 
affect  the  applicability  of  Le  Chatelier's  formula  as  used. 


218 


HIGH   TEMPERATURES. 


opening  c?0,  which  gives  equality  of  brightness  of  the  stand- 
ard candle  with  that  of  the  comparison-lamp,  and  the 
absorbing  power  k  of  the  tinted  glasses,  one  may,  as  was 
said  before,  prepare  a  table  which  gives  directly  the  tem- 
perature corresponding  to  each  aperture  of  the  cat's-eye. 


0 

5 
* 

3 
» 

~*  1 

it, 

*•! 
•*2 
-3 

•r4 

—  R 

^*,~ 

^ 

,''*' 

*^^ 

X 

t 

/ 

/ 

/ 

/ 

f 

/ 

/ 

7 

/ 

/ 

/ 

2.9      3       3.1      3.3      3.3      3.4-     3.5      3.f>      3.7      3.8      3.'J 
Log.  (2+273J 

FIG.  49. 


With  an  apparatus  for  which 


the  following  table  is  obtained,  in  which  the  plus  sign 
refers  to  tinted  glasses  placed  before  the  objective,  and  the 
minus  sign  to  those  before  the  comparison-lamp. 

This  graduation  applies  to  all  bodies  placed  in  an  en- 
closure at  the  same  temperature,  in  the  interior  of  fur- 


OPTICAL  PYROMETER.  219 

naces  for  example,  and  to  black  bodies  whatever  the  tem- 
perature surrounding  them;  for  example,  it  applies  very 
closely  for  a  piece  of  red-hot  iron  exposed  to  the  free  air. 
For  bodies  whose  emissive  power  is  inferior  to  unity,  as 
platinum,  magnesia,  lime,  it  is  necessary,  when  they  are 
exposed  to  the  air  and  not  surrounded  by  an  enclosure 
at  the  same  temperature,  to  make  a  special  graduation. 


nperatures. 

-2  Glasses.  -1  Glass.       0  Glass. 

+  1  Glass. 

+  2  Glasses. 

700° 

173 

800  

6.9           23.0 

...» 

• 

900 

11.0           

1000  

5.6           18.6 



1100  

10.5 

.  .  « 

•  •  •  » 

1200  

6.5 

.... 

•  »•  • 

1300  

4.0 

13.6 

.  .  .  • 

1400  

9.4 

.  .  «  • 

1500 

.  .  .  .            ...» 

6.6 

.  .  .  • 

1600  

' 

4.8 

1700  

3.6 

12.0 

1800  

9.1 

1900  

7.3 

2000  

5.9 

Le  Chatelier  and  Boudouard  have  made  a  series  of 
measurements  on  radiations  of  different  wave  lengths. 
The  junction  of  a  thermoelectric  couple  was  placed  in  a 
small  platinum  tube,  to  realize  approximately  an  enclosed 
space.  By  taking  as  unity  the  brightness  of  melting 
platinum,  the  results  obtained  are  the  following  for  the 
red,  green,  and  blue  radiations: 

t        Log  «  + 273)         Ir          Log/r          Iv  Log/r          7ft          Log  Ib 


900° 

3 

.0707 

0.0000 

4 

.95 

0 

.00018 

4.25 

0.00002 

5 

.3 

1180 

3 

161 

.0024 

8. 

88 

,0087 

3.94 

.0015 

3 

.17 

1275 

3 

190 

.075 

'2 

78 

037 

2.57 

.013 

a 

.11 

1430 

3 

230 

.23 

I 

36 

16 

1.67 

.058 

a 

.76 

1565 

3 

265 

.72 

1 

,86 

47 

1.20 

.24 

1 

.38 

1715 

3 

300 

1.69 

0 

23 

1, 

45 

0.16 

.9 

0 

.95 

220  HIGH  TEMPERATURES. 

Evaluation  of  Temperatures. — Finally,  Le  Chatelier  has 
used  his  optical  pyrometer  to  determine  the  very  highest 
temperatures  realized  in  some  of  the  most  important 
phenomena  in  nature  and  in  the  industries.  These  results, 
quite  different  from  previous  determinations,  were  at  first 
regarded  with  considerable  reserve;  they  are  admitted 
to-day  as  exact,  at  least  within  the  limits  of  precision. 
Here  are  some  of  the  figures  obtained: 

Siemens-Martin  furnace 1490°  to  1580°  C. 

Furnace  of  glass-works 1375  to  1400 

Furnace  for  hard  porcelain 1370 

"   new  porcelain 1250 

Incandescent  lamp 1800 

Arc  lamp 4100 

Sun 7600 

This  determination  of  the  temperature  of  the  sun,  gen- 
erally believed  to  be  low  at  the  time  it  was  found,  has 
been  confirmed  by  the  more  recent  experiments  of  Wilson 
and  Gray  (p.  194)  by  a  totally  different  method.  Later 
determinations  of  the  sun's  temperature,  using  the  re- 
cently established  laws  of  radiation  (Chapter  VII),  give 
values  between  5500°  and  6500°. 

A  series  of  measurements  were  made  with  the  same 
apparatus  in  iron-works.  Here  are  some  results: 

BLAST-FURNACE    SMELTING    GRAY    PIG. 

Opening  before  the  tuyere 1930°  C, 

Tapping  the  pig  iron,  beginning 1400 

"      "       "    end 1520 

BESSEMER    CONVERTER. 

Pouring  the  slag 1580° 

"          "   steel  into  the  ladle 1640 

"         "       "      "       "  moulds 1580 

Reheating  of  the  ingot 1200 

End  of  the  hammering 1080 


OPTICAL  PYROMETER.  221 

SIEMENS-MARTIN  FURNACE. 

Flow  of  the  steel  into  the  ladle,  beginning 1580° 

"     "     "      "       "       "       "       end 1420 

"     hito  the  moulds 1490 

Calibration  in  Terms  of  Wien's  Law. — As  approximately 
monochromatic  radiation  is  used,  the  Le  Chatelier  optical 
pyrometer  may  be  calibrated  in  terms  of  Wien's  law  III 
(p.  183)  by  sighting  upon  a  black  body  (p.  173)  whose  tem- 
perature is  given  by  means  of  a  thermocouple.  For  this 
purpose  Wien's  law  may  be  written: 

log  J=.Xt+Xii, 

where  J  is  the  intensity  of  light,  in  terms  of  the  centre  of 
the  Hefner  flame  for  example,  and  T  is  the  absolute  tem- 
perature. This  method  of  graduation  has  the  advan- 
tage that  only  two  points  are  required  to  completely 
calibrate  the  instrument,  for  the  relation  between  log  J 

and  -=-  is  linear,  so  that  these  quantities  being  plotted 

give  a  straight  line  which  may  evidently  be  extended 
to  lower  and  higher  temperatures,  since  Wien's  law  has 
been  shown  (p.  183)  to  hold  over  the  widest  temperature 
interval  measurable,  provided  the  light  used  is  monochro- 
matic and  the  bodies  observed  approximate  blackness  and 
are  not  luminescent,  that  is,  their  light  not  produced  by 
chemical  or  electrical  excitation. 

Precision  and  Sources  of  Error. — We  shall  give  in  some  de- 
tail a  discussion  of  the  factors  which  in  the  use  of  the  Le 
Chatelier  optical  pyrometer  may  influence  the  photometric 
settings  and  so  affect  the  accuracy  of  temperature  deter- 
minations, as  results  of  such  a  discussion  are  illustrative 
of  what  may  be  expected  from  optical  pyrometers  in 
general.  The  results  are  taken  from  those  of  Waidner 


222  HIGH  TEMPERATURES. 

and  Burgess,  who  have  made  an  experimental  comparison 
of  all  the  available  optical  pyrometers. 

The  sources  of  error  of  this  instrument  may  be  those 
due  to  the  standard  Hefner  amyl-acetate  or  other  stand- 
ard, the  oil  comparison-lamp,  the  focussing  system,  the 
nature  of  the  red  glass  used,  and  the  coefficients  of  absorp- 
tion of  the  glasses  used.  The  first  of  these  affects  only 
comparative  results  with  different  instruments,  while  the 
others,  if  they  exist,  may  be  of  considerable  importance 
in  work  with  a  single  instrument.  We  shall  consider 
them  in  the  order  named. 

As  only  the  central  portion  of  the  amyl-acetate  flame  is 
used,  variations  in  height  and  fluctuations  in  total  intensity 
due  to  various  causes  such  as  moisture  and  carbonic  acid 
in  the  atmosphere  and  changes  due  to  differing  samples 
of  acetate  become  almost,  if  not  quite,  insignificant  in 
this  method  of  comparison ;  so  that  when  using  only  a  small 
central  area  of  the  amyl-acetate  flame,  it  is  a  very  per- 
fectly reproducible  standard  under  the  most  varying 
conditions  of  burning.  Again,  the  effects  of  any  slight 
fluctuations  in  light-intensity  are  further  greatly  reduced 
when  transformed  into  temperature  changes  as  has  been 
shown  (p.  171).  Thus,  the  effect  of  varying  the  height  of  the 
Hefner  flame  by  one  millimeter,  which  amounts  to  ten 
per  cent  of  the  total  intensity  when  the  whole  flame  is 
used,  causes  a  change  of  less  than  one  per  cent  in  the 
intensity  of  light  from  the  central  area,  which  is  equiva- 
lent to  less  than  0°.5  C.  change  in  temperature  at  1000°  C. 

Although  used  intermittently  as  above  indicated,  the 
Hefner  serves  well  enough  as  an  ultimate  standard  by 
means  of  which  the  indications  of  all  photometer-pyrom- 
eters may  be  reduced  to  a  common  basis,  yet  the  Hefner 
is  not  suited  for  use  as  comparison-lamp  in  the  pyrometer 
itself,  as  has  been  previously  stated. 


OPTICAL  PYROMETER. 


223 


In  a  study  of  the  constancy  of  the  comparison-lamp 
the  following  arrangement  was  adopted :  In  order  to  ob- 
tain a  perfectly  constant  source  of  light  with  which  to 
compare  the  flame,  a  32  c.p.  incandescent  electric  lamp 
was  placed  in  a  fixed  position  before  the  objective  of 
the  pyrometer  and  a  glass  diffusing  screen  inserted 
before  the  objective.  The  voltage  across  the  lamp  ter- 
minals was  kept  rigorously  constant  thus  giving  an  arbi- 
trary but  invariable  standard  of  illumination. 

The  concordance  of  results  obtained  by  different  ob- 
servers setting  the  gasolene  flame  and  observing  is  shown 
below: 


WITHOUT   ABSORPTION-GLASS. 


1 

2 

3 

4 

7.4 

7.8 

7.6 

7.3 

7.4 

7.9 

7.8 

7.0 

Cat's-eye  scale  readings.  .  .  • 

7.2 
7.8 

7.7 
7.8 

7.6 

7.7 

8.0 
7.1 

7.7 

7.7 

7.8 

8.3 

.7.8 

7.7 

7.4 

8.0 

Means. 


7.55     7.73     7.65    7.60 


Observers  Nos.  2  and  4  had  no  experience  in  the  use  of 
the  instrument. 


WITH    ABSORPTION-GLASS. 


Observer  

1 

3 

25.7 

25.8 

24.0 

24.8 

23.6 

26.0 

Cat's-eye  scale  readings.  .  . 

24.1 

25.8 

25.4 

24.8 

24.8 

24.9 

24.8 

25.3 

Means...  24.63 


25.34 


224  HIGH   TEMPERATURES. 

Here  the  greatest  variation  corresponds  to  less  than  three 
degrees  in  temperature  at  1000°  C. 

To  control  accurately  the  flame  height  in  the  gasolene 
lamp,  a  sight  was  inserted  consisting  of  a  horizontal  scratch 
2  mm.  above  the  window  before  the  flame,  and  a  very  fine 
platinum  wire  in  the  same  horizontal  plane  but  in 
a  collar  behind  the  flame.  With  this  improvement  an 
observer  can  set  and  control  the  flame-height  to  0.2  mm. 
Such  provision,  however,  is  not  necessary  except  in  the 
most  refined  work,  for  experiment  showed  that  for  most 
purposes  changes  of  over  2  mm.  may  be  made  in  the 
flame  height  with  unimportant  changes  resulting  in  the 
temperature  estimation. 

Considering  the  time-effect  of  burning  upon  the  flame- 
height  and  intensity  due  to  local  heating  and  change  of 
depth  of  oil,  it  was  found  that  the  flame  ceases  creeping 
up  after  ten  minutes  and  will  then  remain  at  constant 
height  to  within  0.5  mm.  until  the  oil  is  used  up,  in  three 
hours,  and  during  all  this  period  the  brightness  of  the 
flame  does  not  change  by  an  amount  corresponding  to 
more  than  5°  in  temperature. 

It  might  be  expected  that  oils  of  different  grades  would 
give  widely  differing  results,  but  an  examination  of  this 
possible  source  of  error  showed  that  different  samples  of 
gasolene  and  gasolenes  mixed  with  several  per  cent  of  a 
heavy  kerosene  gave  identical  results.  This  is  of  great 
importance  in  the  practical  use  of  the  instrument  as  it 
shows  that  a  calibration  made  with  a  given  sample  of  gaso- 
lene remains  good  for  any  other  gasolene. 

From  the  above  it  is  clear  that  variations  in  brightness 
of  the  comparison-flame  due  to  all  possible  causes  need 
not  produce  errors  in  temperature  measurement  of  over 
5°C.  at  1000°  C.,  that  is  within  the  experimental  limits 
of  making  the  photometric  setting, 


OPTICAL  PYROMETER.  225 

Considering  now  the  sources  of  error  due  to  focussing 
and  sighting  upon  the  object  whose  temperature  is  sought, 
it  is  first  to  be  noticed  that  there  is  a  minimum  distance 
from  the  object  at  which  the  pyrometer  can  be  focussed, 
this  distance  being  somewhat  over  a  meter,  depending,  of 
course,  upon  the  focal  length  of  the  objective  and  length 
of  draw-tube.  There  is  also  a  minimum  area  which  can 
be  sighted  upon  and  give  an  image  of  sufficient  size  to 
completely  cover  the  desired  photometric  field ;  this  mini- 
mum size  of  object  is  about  6  mm.  on  a  side  when  the 
instrument  is  at  its  least  distance;  for  greater  distances 
a  larger  area  must  be  viewed. 

The  draw-tube  can  easily  be  set  to  2  mm.  when  focussing, 
and  as  the  image  is  over  20  cm.  from  the  objective  in  all 
cases,  the  resulting  error  in  intensity  due  to  focussing  is 
not  greater  than  2  per  cent.  This  corresponds  to  1°  C. 
in  temperature,  showing  that  an  error  of  even  5  mm.  in 
focussing  the  draw-tube  will  not  produce  an  appreciable 
error  in  temperature  estimation. 

Often,  in  use,  the  distance  of  the  instrument  from  the 
objects  studied  needs  to  be  changed  considerably,  and 
in  rapid  work  it  is  not  always  convenient  to- refocus;  a 
change  in  this  distance  of  a  fourth  of  its  value,  i.e.,  from 
120  cm.  to  150  cm.,  will  produce  an  apparent  change  in 
intensity  of  only  9  per  cent,  or  about  5°  C.  in  temperature. 
That  these  errors  of  focussing  are  so  small  when  inter- 
preted into  temperatures,  showing  that  no  unusual  pre- 
cautions are  needed,  is  evidently  of  great  convenience  in 
the  use  of  the  instrument. 

The  non-monochromatism  of  the  red  glass  in  the  eye- 
piece produces  no  considerable  error  in  temperature- 
measurement  up  to  1600°  C.,  although  if  this  glass  is  not 
very  nearly  monochromatic  the  differences  in  hue  in 
the  two  adjacent  photometric  fields— from  the  compari- 


226  HIGH  TEMPERATURES. 

son-lamp  and  other  sources — are  very  troublesome,  and 
the  strain  on  the  eye  in  matching  them  is  considerable.  For 
the  best  work  at  high  temperatures  a  better  glass  than  is 
usually  furnished  with  the  instrument  must  be  used. 

There  remains  to  be  considered  the  error  introduced  due 
to  uncertainty  in  the  knowledge  of  the  coefficient  of  absorp- 
tion of  the  absorbing-glasses.  If  an  observation  (Nf)  is 
taken  with,  and  then  one  (N)  without,  an  absorption-glass, 
we  have 


so  that  the  accuracy  in  determining  k  depends  directly 
upon  the  precision  of  setting  and  reading  the  cat's-eye 
opening.  Errors  of  over  5°  at  1000°  C.  can  hardly  occur 
from  this  cause,  although  the  determination  of  k  is  the 
most  difficult  and  uncertain  of  all  the  operations  in  opti- 
cal pyrometry. 

Modifications  of  the  Le  Chatelie'r  Pyrometer. — For  use  in 
technical  works  and  other  places  where  there  are  sure  to 
be  strong  drafts  of  air  causing  unsteadiness  of  the  flame  of 
the  oil  comparison -lamp,  the  Le  Chatelier  pyrometer 
might  be  improved  by  the  substitution  of  an  electric 
incandescent  lamp  of  low  voltage  (six)  placed  before  a 
uniformly  ground  diffusing-glass  screen,  which,  illumi- 
nated by  the  incandescent  lamp,  becomes  the  constant 
comparison  source.  The  electric  lamp  may  be  mounted 
in  a  vertical  arm  which  serves  at  the  same  time  as  a 
handle,  and  then  the  instrument  becomes  as  portable  as 
an  opera-glass.  The  reliability  of  such  a  method  of  pro- 
ducing a  comparison-light  of  invariable  intensity  will 
be  discussed  when  describing  the  Wanner  instrument. 
Other  modifications  will  be  discussed  under  the  Fery  and 
Warmer  pyrometers. 


OPTICAL  PYROMETER. 


227 


Fe*ry  Absorption-pyrometer. — This  is  identical  with  Le 
Chatelier's  instrument,  except  that  a  pair  of  absorbing- 
glass  wedges  p,  p'  replaces  the  iris  diaphragm,  and  the  45° 


"T         A         f    V 


1IZZ 


/  \- 


\    / 


•J 


Fia.  50. 


mirror  G,  with  parallel  faces,  is  silvered  over  a  narrow 
vertical  strip,  giving  a  photometric  field  of  form  shown 


228  HIGH  TEMPERATURES. 

at  ab,  when  looking  at  a  hot  crucible.  The  instrument  has 
a  fixed  angular  aperture,  so  that  no  correction  has  to 
be  made  for  focussing  or  for  varying  distance  from  furnace. 
The  comparison-light  L  plays  the  same  role  as  in  Le  Chate- 
lier's  pyrometer,  and  the  range  of  the  instrument  may  be 
similarly  extended  by  the  use  of  auxiliary  absorbing- 
glasses.  Fery  has  in  addition  made  his  instrument  mov- 
able about  a  horizontal  axis,  which  is  a  convenience. 

The  calibration  is  equally  simple.  If  x  is  the  thickness 
of  the  wedges,  read  off  on  a  scale,  when  the  light  from 
the  comparison-lamp  and  furnace  is  of  the  same  bright- 
ness, then  the  relation  between  brightness  /  and  thickness 
of  wedge  is 


where  k  is  the  coefficient  of  absorption  of  the  glass  of  the 
wedges  for  the  red  light  used  and  c  is  a  constant. 

But  by  Wien's  law  III  (p.  183),  assuming  it  to  apply 
here, 

B 


or  combining  these  two  equations  we  have 


whence 


Thus  it  follows  that  the  thickness  of  the  wedge  is  in- 
versely proportional  to  the  absolute  temperature,  so  that 
the  calibration  may  be  effected  by  finding  the  thickness 
of  wedge  for  two  temperatures  only  and  plotting  a  straight 
line  and  constructing  a  table  giving  /  and  T  respectively 
in  terms  of  x. 


OPTICAL  PYROMETER.  229 

It  is  questionable  if  there  is  any  gain  in  substituting 
the  wedge  for  the  cat's-eye  in  the  desire  to  extend  the 
range  over  which  the  instrument  may  be  used  without 
employing  the  auxiliary  absorbing-glasses,  for  thereby 
the  sensibility  is  somewhat  reduced,  and  more  important 
still,  the  wedge  instrument  cannot  be  used  at  such  low 
temperatures  as  the  original  Le  Chatelier  form,  nor  is 
there  any  gain  in  simplicity  of  calibration  and  ease  of 
manipulation.  The  shape  of  the  photometric  field,  the 
use  of  an  aperture  of  constant  angle,  and  making  the 
instrument  movable  about  a  horizontal  axis,  however, 
are  improvements  which  may  be  applied  with  advantage 
to  the  Le  Chatelier  instrument. 

Wanner  Pyrometer.  —  Description  and  Calibration.  — 
Wanner,  making  use  of  the  polarizing  principle  discarded 
by  Le  Chatelier,  has  brought  out  a  photometer-pyrometer 
which  is  a  modification,  suited  to  temperature-measure- 
ments, of  Konig's  spectrophotometer.* 

The  comparison-light  is  a  six-volt  incandescent  lamp, 
illuminating  a  glass-matt  surface;  monochromatic  red 
light  is  produced  by  means  of  a  direct-vision  spectroscope 
and  screen  cutting  out  all  but  a  narrow  band  in  the  red, 
and  the  photometric  comparison  is  made  by  adjusting  to 
equal  brightness  both  halves  of  the  photometric  field  by 
means  of  a  polarizing  arrangement. 

The  slit  St  is  illuminated  by  light  from  the  comparison 
source  reaching  S^  after  diffuse  reflection  from  a  right- 
angled  prism  placed  before  Sv  Light  from  the  object 
whose  temperature  is  sought  enters  the  slit  S2.  The  two 
beams  are  rendered  parallel  by  the  lens  Llt  and  each  .dis- 
persed into  a  continuous  spectrum  by  the  direct-vision 
prism  P.  Each  of  these  beams  is  next  separated  by  a 

*  Konig,  Wied.  Ann.,  53,  p.  785,  1894. 


230 


HIGH   TEMPERATURES. 


\ 


Rochon  prism  R  into  two  beams,  polar- 
ized in  planes  at  right  angles.  Con- 
sidering only  the  red  light,  there  would 
now  be  four  images  formed  by  the  lens 
L2,  and  distributed  about  the  slit  £4. 
In  order  to  bring  two  red  images  oppo- 
sitely polarized  exactly  before  this  slit, 
a  bi-prism  B  is  interposed  whose  angle 
is  such  as  to  effect  this  for  two  images 
only,  at  the  same  time  increasing  the 
number  of  images  to  eight.  There  is 
now  in  the  field  of  view  before  the 
Nicol  analyzer,  A,  two  contiguous  red 
fields  composed  of  light  oppositely 
polarized,  the  light  of  one  coming  from 
Sl  alone,  and  of  the  other  from  S2  alone. 
All  the  other  images  are  cut  off  from 
the  slit  S4.  If  the  analyzer  is  at  an 
angle  of  45°  with  the  plane  of  polariza- 
tion of  each  beam,  and  if  the  illumina- 
tion of  S1  and  S2  is  of  the  same  bright- 
ness, the  eye  will  see  a  single  red  field 
of  uniform  brightness.  If  one  slit  re- 
ceives more  light  than  the  other,  one- 
half  of  the  field  will  brighten,  and  the 
two  may  be  brought  to  equality  again 
by  turning  the  analyzer  carrying  a 
graduated  scale,  which  may  be  cali- 
brated hi  terms  of  temperature. 

If  the  analyzer  is  turned  through 
an  angle  <j>  to  bring  the  two  halves  of 
the  field  to  the  same  brightness,  the 
relation  between  the  two  intensities 
from  Sl  and  S2  is 


OPTICAL  PYROMETER.  231 

i-tanV-      .'•-'.     •     •     •     («) 

t/2 

Since  monochromatic  light  is  used,  and  the  comparison- 
beam  and  that  from  the  object  examined  undergo  the 
same  optical  changes,  Wien's  law  III  may  form  the  basis 
of  the  calibration. 

If  JQ  is  the  intensity  of  the  light  from  the  standard 
and  J  that  from  the  object  whose  temperature  is  sought, 
Wien's  law  III  gives 


'°7 


l      l\ 

T~YJ 


Since  the  constant  C=  14,500  for  a  black  body  and  ^= 
0.656/z  as  the  instrument  is  usually  constructed,  a  knowl- 
edge of  the  apparent  black-body  temperature  of  the 
standard  source,  together  with  the  reading  of  the  analyzer- 
scale  at  the  normal  point  when  J=J0,  for  such  an  instru- 
ment, is  all  the  data  required  for  its  calibration,  as  any 
temperature  may  then  be  calculated  by  means  of  equa- 
tions (a)  and  (6)  in  terms  of  the  scale-readings.  This 
instrument  may  also  of  course  be  empirically  calibrated 
against  a  thermocouple  using  a  black  body  to  sight  upon. 
It  is  evidently  necessary  to  be  able  to  always  reproduce 
exactly  the  standard  intensity  J0.  Now  the  brightness 
of  an  electric  lamp  will  vary  with  the  current  through 
it,  so  it  is  necessary  to  check  frequently  the  constancy 
of  illumination  of  the  slit  S^  against  a  standard  source 
of  light.  An  amyl-acetate  lamp  and  a  ground-glass 
diffusing-screen  can  be  placed  before  the  slit  S2,  thus  fur- 
nishing the  standard  light  required.  The  analyzer  is 
then  set  at  the  previously  determined  normal  point  and 
the  distance  of  the  electric  lamp  from  Sl  adjusted  or  the 


232 


HIGH   TEMPERATURES. 


current  through  the  lamp  changed  by  a  rheostat,  until 
the  two  fields  appear  of  the  same  brightness. 

Sources  of   Error. — A  study  of  a  Wanner  instrument 
by  Waidner  and  Burgess  has  led  them  to  the  following 


FIG.  52. 

conclusions.  The  sensibility  of  this  pyrometer  varies 

with  change  in  the  angle,  and  is  so  adjusted  as  to  be  the 

greatest  between  1000°  and  1500°  C.  and  is  about  as 
follows : 

0 . 1  scale  div.  1°  C.  at  1000°  C. 

0 . 1  scale  div.  2°  C.  at  1500°  C. 

0, 1  scale  div.  7°  C.  at  1800°  C. 

The  reproducibility  of  the  brightness  of  the  amyl-acetate 
flame  as  viewed  through  the  ground-glass  diffusing- 
screen  is  a  measure  of  the  ability  of  the  instrument  to 
repeat  its  indications.  It  is  very  important  that  this 
diffusing-screen  be  always  placed  in  exactly  the  same 
position  relative  to  the  flame  and  slit  S2,  and  further 
that  it  be  free  from  dust  and  finger-marks.  These  require- 
ments can  only  be  satisfactorily  met  by  protecting  this 


OPTICAL  PYROMETER  233 

screen  by  a  cover-glass  and  providing  an  adjustment 
for  setting  it  exactly  in  place  between  the  flame  and 
slit. 

The  constancy  of  the  amyl-acetate  flame  as  used  with 
this  pyrometer  under  ordinary  conditions  of  burning  is 
illustrated  by  the  following  set  of  observations,  during 
which  the  current  through  the  electric  comparison-lamp 
was  kept  rigorously  constant  by  means  of  a  milliamnieter 
and  rheostat: 

Reading  of  Instrument. 
39.9 
39.9 
40.1 
39.9 
39.1 
39.2 
39.8 
39.0 


39.6  0.38 

This  shows  that  the  flame  can  be  relied  upon  to  give  an 
intensity  of  illumination  whose  constancy  expressed  in 
terms  of  temperature  is  0.5  per  cent.  Variations  in 
height  of  the  flame,  if  they  do  not  exceed  2-3  mm.,  together 
with  fluctuations  in  atmospheric  conditions,  will  not 
produce  errors  in  temperature  estimation  exceeding  1 
per  cent. 

The  uncertainty  of  setting  the  nicol,  due  to  lack  of 
sensitiveness  of  the  eye  to  exactly  match  the  two  halves 
of  the  photometric  field,  is  also  about  1  per  cent,  or  slightly 
better  with  practice. 

The  adjustment  of  the  electric  lamp  to  standard  intensity 
at  the  point  on  the  scale  chosen  as  normal  point  can  be 
made,  when  proper  care  is  taken  regarding  the  diffusing- 
screen,  to  1  per  cent  expressed  in  temperature  change. 


234 


HIGH   TEMPERATURES. 


This  source  of  error  does  not  effect  relative  results  in  any 
one  series  for  one  setting  to  the  normal  point. 

The  "most  serious  source  of  error,  except  when  special 
precautions  are  taken,  is  the  variation  in  brightness  of 
the  electric  comparison-lamp  due  to  variation  in  the  cur- 
rent furnished  by  the  three-cell  storage-battery. 

With  the  10-ampere-hour  battery  furnished  with  the 
Wanner  instrument,  after  making  circuit  the  electro- 
motive force  drops  by  about  2  per  cent  in  two  minutes 
and  then  falls  off  slowly,  but  nearly  recovers  the  original 
voltage  after  remaining  on  open  circuit  even  for  a  very 
short  time.  When  the  battery  is  in  good  condition 
the  variation  in  three  hours  at  normal  discharge  (0.075 
ampere)  is  about  0.08  volt,  and  somewhat  less  for  the 
current  (0.55  ampere)  taken  by  the  lamp;  with  the  battery 
in  poor  condition  these  changes  are  much  accentuated. 

The  following  table  illustrates  the  effect  of  slight  varia- 
tions in  current  through  the  lamp  on  apparent  tempera- 
ture of  the  amyl-acetate  flame,  for  the  small  battery  of 
10  ampere-hours  furnished  with  the  instrument.  The 
apparent  change  in  temperature  is  calculated  from  the 
current  change: 


SMALL    BATTERY. 


Time, 
Minutes. 

Wanner  Scale. 

Current. 

Per  Cent 
Change  in 
Current. 

Apparent 
Change  in 
Temp. 

15 

31.2 

0.5645 

20 

31.8 

0.5640 

0.1 

1°C. 

27 

32.7 

0.5550 

1.7 

10 

37 

34.6 

0.5400 

4.3 

25 

3ft 
40 

Disconnecte 
32.5 

d  battery  two 
0.5610 

minutes. 
0.6 

3 

42 

31.7 

0.5570 

1.5 

7 

45 

32.5 

0.5560 

2.5 

15 

47 

33.1 

0.5505 

4.1 

24 

OPTICAL  PYROMETER.  235 

A  battery  of  75  ampere-hours  gave  similar  results. 

The  above  results  give  abundant  evidence  of  the  need 
of  maintaining  the  current  through  the  lamp  quite  con- 
stant in  work  of  precision.  A  series  of  experiments  has 
shown  that  in  the  range  1000°- 1500°  C.  one  division  on  the 
Wanner  scale  corresponds  to  about  0.009  ampere,  or  1°  C. 
apparent  change  in  temperature  is  produced  by  a  fluctua- 
tion of  0.0012  ampere  through  the  lamp;  hence  to  obtain 
a  precision  of  5°  the  current  must  be  kept  constant  to 
0.01  of  its  value.  The  above  table  shows  that  this  is  by 
no  means  effected  by  using  the  battery  without  regulating 
the  current,  for  even  with  the  battery  in  the  best  condi- 
tion the  current  increases  by  2  per  cent  in  the  first  eight 
or  nine  minutes  of  discharge  and  then  falls  off  1  per  cent 
in  the  next  twenty  minutes.  The  temperature  coefficient 
of  the  battery  would  produce  only  insignificant  changes. 
The  table  shows  further  that  breaking  the  circuit  and  then 
making  it  again  may  cause  an  apparent  temperature 
change  of  over  20°  C.  For  work  of  precision,  therefore, 
it  is  essential  to  keep  the  current  constant  by  means  of 
a  milliammeter  and  rheostat,  otherwise  uncertainties  of 
over  25°  C.  will  occur  in  the  temperature  measurements. 
These  will  increase  with  the  battery  in  poor  condition. 

Range  and  Limitations. — The  above  description  of  the 
Wanner  pyrometer  has  shown  the  great  loss  of  light  due 
to  the  optical  system  employed.  This  prevents  measuring 
temperatures  below  about  900°  C.  (1650°  F.)  with  this 
instrument.  There  is  no  method  of  sighting  this  pyrom- 
eter exactly  upon  the  spot  desired,  except  by  trial,  as  no 
image  of  the  object  examined  is  formed  in  the  eye-piece, 
but  this  inconvenience  is  in  part  compensated  by  not 
having  to  focus  with  varying  distance  from  the  object. 

There  is  another  limitation  which  may  in  certain  cases 
become  a  serious  source  of  error; — light  from  incandes- 


236  HIGH   TEMPERATURES. 

cent  surfaces  is  in  general  polarized  and,  as  the  Wanner 
instrument  is  a  polarizing  pyrometer,  care  must  be  taken 
to  eliminate  this  source  of  error  when  it  exists. 

If  an  incandescent  object  is  viewed  normally  the  amount 
of  polarized  light  is  very  small,  but,  as  the  angle  of  inci- 
dence increases,  the  proportion  of  light  polarized  becomes 
greater  and  greater.  Besides  varying  with  the  angle  of 
incidence,  the  amount  of  polarized  light  emitted  varies 
widely  with  different  substances,  being  greatest  for  polished 
platinum  and  very  much  less  for  iron,  glass,  etc.  In  some 
measurements  made  with  the  Wanner  pyrometer  on  the 
temperature  of  an  incandescent  platinum  strip  in  the 
neighborhood  of  1350°  C.,  Waidner  and  Burgess  have  found 
a  maximum  difference  in  the  readings  of  90°  C.  for  posi- 
tions of  the  instrument  at  right  angles  to  one  another  in 
azimuth  and  for  an  angle  of  incidence  of  70°  with  the 
normal  to  the  surface.  This  introduces,  under  these 
conditions,  the  possibility  of  an  error  of  45°  C.  in  the  tem- 
perature-measurement. This  source  of  error  can  be 
eliminated  by  taking  the  mean  of  four  readings  for  azi- 
muths 90°  apart.  The  magnitude  of  the  error  arising 
from  this  cause  is  entirely  negligible  for  all  practical  pur- 
poses for  many  substances,  such  as  iron,  porcelain,  etc. 

A  review  of  the  sources  of  error  and  limitations  of  the 
Wanner  pyrometer  shows  that  they  may  exert  a  rela- 
tively great  effect  on  the  temperature-measurements,  and 
it  was,  therefore,  thought  worth  while  to  emphasize  them, 
but  on  the  other  hand  they  may  all  be  practically  elimi- 
nated with  reasonable  care,  and  the  instrument  then  be- 
comes one  of  great  precision  and  convenience. 

Holborn  and  Kurlbaum,  and  Morse,  Pyrometers. — If 
a  sufficient  current  is  sent  through  the  filament  of  an 
electric  lamp  the  filament  glows  red  at  first,  and  as  the 
current  is  increased,  the  filament,  getting  hotter  and 


OPTICAL  PYROMETER. 


237 


hotter,  becomes  orange,  yellow,  and  white,  just  as  any 
progressively  heated  body.  If  now  this  filament  is  inter- 
posed between  the  eye  and  an  incandescent  object,  the 
current  through  the  lamp  may  be  adjusted  until  a  portion 
of  the  filament  is  of  the  same  color  and  brightness  as  the 
object.  When  this  occurs  this  part  of  the  filament  becomes 
invisible  against  the  bright  background,  and  the  current 
then  becomes  a  measure  of  the  temperature  as  given 
either  by  a  thermocouple  or  in  terms  of  the  intensity  of 
illumination. 

Holborn  and  Kurlbaum  Form. — A  small  four- volt  electric 
incandescent  lamp  L  with  a  horseshoe  filament  is  mounted 
in  the  focal  plane  of  the  objective  and  of  the  eye-piece  of  a 
telescope  provided  with  suitable  stops  D,  D,  D,  and  a 
focussing  screw  S  for  the  objective.  The  lamp  circuit  is 
completed  through  a  two-cell  storage  battery  B,  a  rheo- 
stat, and  a  milliammeter. 


Section  oilA-0 


45  Mirror 
Absorbing  Screen 


Milli  Ammeter 


The  determination  of  a  temperature  consists  in  focus- 
sing the  instrument  upon  the  incandescent  object,  thus 
bringing  its  image  into  the  plane  AC,  and  adjusting  the 


238  man  TEMPERATURES. 

current  by  means  of  the  rheostat  until  the  tip  of  the  lamp 
filament  disappears  against  the  bright  background,  when 
a  previous  calibration  of  current,  in  terms  of  temperature 
for  the  particular  lamp  used,  gives  the  temperature  by 
reading  the  milliammeter. 

As  the  temperature  of  the  filament  increases,  the  effect 
of  irradiation  or  too  great  brightness  becomes  blinding, 
and  the  photometric  comparison  is  then  rendered  possible 
at  these  temperatures  by  the  introduction  of  one  or  more 
monochromatic  red  glasses  before  the  eye-piece,  giving 
as  well  all  the  advantages  of  photometry  of  a  single  color. 
Below  800°  C.  the  measurements  are  more  easily  made 
without  any  red  glass,  as  the  filament  itself  is  then  red 
and  the  lowest  temperatures  are,  of  course,  reached  with 
the  least  interposition  possible  of  absorbing  media.  The 
lower  limit  of  the  instrument  is  very  nearly  600°  C.  Two 
red  glasses  are  required  for  temperatures  above  1200°  C., 
and  for  very  high  temperatures  it  is  necessary  in  order  to 
avoid  overheating  the  lamp  filament  by  the  current  to 
put  absorbing-glasses  or  a  double-prism  mirror  (Fig.  53) 
before  the  objective,  and  they  also,  of  course,  require 
calibration.  At  very  high  temperatures,  unless  a  strictly 
monochromatic  glass  is  used,  the  pyrometry  becomes 
difficult,  the  filament  never  disappearing  completely. 

The  coefficient  of  absorption  of  the  prism  system  or  of 
an  absorbing-glass  may  be  calculated  by  making  use  of 
Wien's  law  (p.  183),  supposing  it  to  hold  for  the  red  glass 
used.  If  K  is  the  reciprocal  of  the  coefficient  of  absorp- 
tion, Tv  T2  the  apparent  temperatures  (absolute)  given 
by  the  pyrometer,  sighting  first  without  and  then  with 
the  absorbing  medium,  then  Wien's  law  III  gives: 

,     J1     C  log  e  i  \       1 
=! - 


OPTICAL  PYROMETER. 


239 


where  C=  14500  for  a  black  body  and  X  is  the  wave  length 
for  the  colored  glass  used.  For  very  high  temperatures, 
although  this  formula  will  give  a  consistent  scale  when  K 
has  been  determined,  yet  the  values  obtained  are  in  error 
by  amounts  depending  upon  the  monochromatism  of  the 
red  glass  used  and  the  departure  of  the  source  from  a 
black  body. 

The  eye  is  particularly  sensitive  in  recognizing  equality 
of  brightness  of  two  surfaces,  one  in  front  of  the  other, 
and  this  pyrometer,  therefore,  provides  a  very  delicate 
means  of  judging  temperatures,  since  the  Iigh1>intensity, 
as  has  been  shown  (p.  171),  varies  so  much  faster  than 
does  the  temperature. 

The  precision  attainable  with  this  pyrometer  is  illus- 
trated by  the  following  series  of  observations  which  are 
indicative  of  the  ordinary  performance  of  the  instrument: 


Temp,  from 
H-&K. 
Pyrometer. 

Temp,  from 
Thermocouple. 

Temp,  from 
H.  &K. 
Pyrometer. 

Temp,  from 
Thermocouple. 

1347 

1347°  C. 

632 

634°  C. 

1351 

1347 

634 

633 

1343 

1343 

633 

633 

1333 

1342 

633 

632 

1342 

1342 

Different  observers  do  not  differ  by  any  appreciable 
amount  in  their  readings,  and  at  low  temperatures  the 
same  values  are  obtained  whether  a  red  glass  is  used  or 
not. 

For  the  calibration  of  the  instrument,  it  is  necessary  to 
find  empirically  the  relation  between  the  current  through 
the  lamp  and  the  temperatures  for  a  number  of  tempera- 
tures, and  then  interpolate  either  analytically,  or,  better, 


240  HIGH  TEMPERATURES. 

graphically.     The  calibration  will  evidently  be  an  inde- 
pendent one  for  each  lamp  used. 

The  relation  between  current  and  temperature  is  suffi- 
ciently well  expressed  by  a  quadratic  formula  of  the  form 

C=a+bt+ct*. 

That  this  formula  gives  satisfactory  results  is  shown 
by  observations  of  Holborn  and  Kurlbaum  for  a  lamp 
satisfying  the  equation 

CIO3  =  170.0  +0. 1600*  +  0.0001333Z2. 

C  amp  t  obs.  t  calc.  At. 

340  686  679  -7°C. 

375  778  778  0 

402  844  850  +6 

477  1026  1032  +6 

552  1196  1196  0 

631  1354  1354  0 

712  1504  1504  0 

The  question  whether  or  not  the  temperatures  indicated 
by  the  lamp  will  repeat  themselves  for  continued  burning 
or  aging  is  a  vital  one  for  the  permanence  of  a  calibra- 
tion and  hence  for  the  practical  usefulness  of  the  pyrom- 
eter. Holborn  and  Kurlbaum  as  well  as  Waidner  and 
Burgess  have  made  a  thorough  study  of  this  possible 
source  of  error. 

Lamps  which  have  not  been  aged  or  burned  for  some 
tune  at  a  temperature  considerably  above  that  at  which 
they  will  ordinarily  be  used,  undergo  marked  changes 
and  are  unreliable,  but,  if  properly  aged,  they  reach  a 
steady  condition,  as  indicated  by  the  following  table  of 
results  obtained  by  Holborn  and  Kurlbaum  on  these 


OPTICAL  PYROMETER.  241 

lamps.     The  current  is  given  in  each  case  for  a  tempera- 
ture of  1100°C. 


AGING   OF  LAMPS. 

Current. 


Lamp  Number 1 

After  20  hours  burning  at  1900°  C 0.608  0.592  0.589 

"       5       "           "        "        "       613  .592  .592 

"       5       "           "        "        "       621  .597  .597 

"      5      "           "        "        "       622  .599  .600 

"     20      "          "        "  1500°  C 622  .599  .601 

If  a  lamp  is  not  aged  its  indications  may  change  by 
as  much  as  25°  C.  with  time,  but  after  twenty  hours' 
heating  at  1800°  it  will  undergo  no  appreciable  further 
changes  over  a  period  of  time  corresponding  to  many 
months  if  used  hi  the  shop,  if  not  heated  above  1500°. 
This  state  of  permanence  is  sufficient  to  satisfy  the  most 
rigid  requirements  of  practice. 

Morse  Form. — This  instrument  is  based  on  exactly  the 
same  principle  as  the  Holborn-Kurlbaum.  It  will  only 
be  necessary  in  describing  it  to  point  out  the  differences 
in  construction  from  the  German  make. 

Instead  of  a  simple  horseshoe  filament,  Morse  uses  a 
large  spiral  filament  in  the  lamp  so  that  in  sighting  upon 
an  incandescent  body  it  is  necessary  to  choose  some 
particular  spot  of  the  spiral  and  try  to  make  that  spot 
disappear.  This  is  fatiguing,  as  the  spiral  covers  a  large 
area  and  is  of  just  sufficiently  varying  color  to  cause  the 
eye  to  wander.  This  effect  is  aggravated  by  the  fact  that 
the  instrument  is  not  a  telescope,  possessing  no  eye-piece 
or  objective,  so  that  the  eye  has  to  accommodate  itself 
back  and  forth  between  the  filament  and  the  object 
studied. 

The    four-volt     battery    for    the    Holborn-Kurlbaum 


242  HIGH  TEMPERATURES. 

lamps  is  here  replaced  by  a  battery  of  forty  or  fifty  volts 
to  run  the  spiral  lamp,  requiring  a  costly  installation. 

The  Morse  instrument  was  designed  for  use  in  harden- 
ing steel,  and,  throughout  the  limited  temperature  range 
required  in  this  process,  in  spite  of  the  crudities  of  con- 
struction above  noted,  this  pyrometer  may  be  read  to 
about  3°  C.  within  this  range.  Above  1100°  C.,  however, 
it  is  very  difficult  and  soon  becomes  impossible  to  make 
a  satisfactory  setting. 

Tests  of  these  spiral-filament  lamps  show  that  when 
aged  at  1200°  C.  they  will  remain  constant  for  several 
hundreds  of  hours  within  the  range  over  which  they  are 
intended  to  be  used. 

It  is  interesting  in  this  connection  to  note  the  behavior 
of  ordinary  incandescent  lamps  as  to  permanence. 


-18 

!r~  — 

-n  . 

C.R 
50          100 

—  -  ^ 

200     HOURS     300                      400    4?£              500" 

A 

FIG.  54. 

Conditions  of  Use. — The  optical  pyrometer,  by  reason  of 
the  uncertainty  of  emissive  powers  and  of  the  relatively 
slight  sensibility  of  the  eye  for  comparisons  of  luminous 
intensities,  cannot  give  as  accurate  results  as  the  electric 
methods,  although  the  accuracy  attainable,  since  the  sat- 
isfactory establishment  of  the  laws  of  radiation  throughout 
practically  the  attainable  temperature  range,  is  sufficient, 
as  we  have  seen,  when  proper  precautions  are  taken,  for 
all  industrial  and  most  scientific  needs. 


OPTICAL  PYROMETER.  243 

The  optical  or  radiation-pyrometer  is  peculiarly  well 
adapted  for  many  cases  in  which  other  methods  fail,  as 
when  contact  with  the  object  whose  temperature  is  sought 
cannot  be  made  or  when  for  any  reason  the  pyrometer 
must  be  placed  at  a  distance;  for  example,  in  the  case  of 
a  moving  body,  as  a  rail  passing  into  the  rolling-mill;  in 
the  case  of  very  high  temperatures  superior  to  the  fusing- 
point  of  platinum,  as  of  the  crucible  of  the  blast-furnace  or 
that  of  the  electric  furnace;  in  the  case  of  isolated  bodies 
radiating  freely  into  the  air,  as  flames  or  wires  heated  by 
an  electric  current  which  cannot  be  touched  without 
changing  their  temperature. 

It  is  also  convenient  in  the  case  of  strongly  heated  fur- 
naces, as  steel  and  porcelain  furnaces.  But  in  this  usage 
care  must  be  taken  to  guard  against  the  brightness  of  the 
flames,  always  hotter  than  the  furnace,  and  against  the 
entry  of  cold  air.  The  arrangement  with  the  closed  tube 
described  in  connection  with  the  heat-radiation  pyrometer 
is  indispensable  if  it  is  desired  to  obtain  anywhere  near 
exact  results.  Compared  to  this  last  pyrometer,  the  optical 
pyrometer  has  the  advantage  to  require  no  installation  in 
a  fixed  position.  It  has,  on  the  other  hand,  the  incon- 
venience to  require  a  more  active  intervention  on  the  part 
of  the  operator  and  can  hardly  be  intrusted  to  a  workman, 
while  the  set-up  of  the  heat-radiation  pyrometer  may  be 
made  so  that  an  observation  reduces  to  a  reading  upon  a 
scale. 

Temperature  of  Flames. — Any  substance  inserted  in  a 
flame  will  take  up  a  lower  temperature  than  that  of  the 
flame  itself,  due  to  conduction,  radiation,  and  diminished 
speed  of  the  gas-stream  around  the  body.  Nichols,  by  using 
thermocouples  of  progressively  finer  wires,  sought  to  deter- 
mine true  flame  temperatures  by  extrapolating  for  a  wire 
of  zero  diameter.  The  uncertainty  of  this  method  is 


244  HIGH  TEMPERATURES. 

considerable  although  it  gives  consistent  results,  which 
are  probably  low. 

The  radiation  methods  have  been  employed  by  Lum- 
mer  and  Pringsheim,  Kurlbaum,  G.  W.  Stewart,  and  Fery. 
The  temperature  as  given  by  an  optical  pyrometer  will 
depend  on  the  thickness  and  density  of  the  flame  as  well 
as  upon  its  reflecting  and  absorbing  powers.  The  reflecting 
power  of  a  flame  is  small  and  probably  varies  with  the 
kind  of  flame;  the  results  as  yet  obtained  are  quite  dis- 
cordant on  this  point. 

Kurlbaum  interposed  a  flame  between  a  black  body 
and  the  eye  and  assumed  that  the  two  were  of  the  same 
temperature  when  the  flame  disappeared  against  its  back- 
ground. This  method  gave  results  lower  than  those 
obtained  by  Lummer  and  Pringsheim  (p.  184).  Kurlbaum 
and  Stewart  both  claim  that  the  carbon  in  the  flame 
departs  more  widely  from  a  black  body  than  platinum, 
and  the  latter  gets  2282  for  the  value  of  A  in  Wien's  dis- 
placement equation  AmT=A,  assuming  Nichols's  value 
1900°  C.  for  the  acetylene  temperature.  Fery  has  shown, 
however,  that  the  brightness  of  the  sodium  line,  measured 
with  a  spectrophotometer,  is  not  increased  by  passing 
obliquely  a  beam  from  an  electric  light  across  the  flame 
studied,  seeming  to  indicate  that  the  diffusing  power  is 
nil  for  the  light  coming  from  carbon.  This  would  imply 
a  value  of  A  of  the  order  of  2800,  or  of  2400°  C.  for  the 
acetylene  flame,  assuming  >1TO  =  1.05. 

Fery's  method  of  measuring  flame  temperatures  is  to 
produce  the  reversal  of  a  metallic  line  by  means  of  light 
emitted  by  a  solid  body  brought  to  the  proper  temperature. 
The  image  of  the  filament  of  an  incandescent  lamp  is 
thrown  by  a  large  aperture  lens  onto  the  narrow  slit  of  a 
spectroscope.  The  rays  from  the  filament  pass  through 
the  flame  to  be  studied,  which  contains  sodium  or  other 


OPTICAL  PYROMETER.  245 

metallic  vapor.  When  the  filament  is  raised  in  tempera- 
ture the  D  line,  say,  is  ultimately  reversed,  and  at  the 
moment  of  disappearance  the  filament  and  flame  are 
assumed  to  have  the  same  temperature,  which  may  be 
measured  by  sighting  an  optical  pyrometer  on  the  filament. 
Some  of  Fery's  results  are  as  follows: 

r  Open  ..........................   1870°C. 

Bunsen  \  Half-open  ......................   1810 

IShut  ...........................   1710 

Acetylene  ...............................  2550 

Oxyhydrogen    with    illuminating-gas     and  )  ^am 
oxygen  ..............................  f 

Oxyhydrogen  with  H,  +  O  ................  2420 


For  this  determination,  Fery  used  his  absorption-pyrom- 
eter. The  results  obtained  may  be  slightly  high,  but 
hardly  by  more  than  100°  C.  ,  as  platinum  may  be  melted 
in  an  open  Bunsen. 

All  of  the  above  methods  assume  that  flames  are  non- 
luminescent,  otherwise  the  results  obtained  are  too  high. 
Absurd  results  will  also  be  obtained  if  the  flames  are  color- 
less, i.e.,  contain  no  finely  divided  particles  heated  by 
the  flame,  as  in  an  open  Bunsen. 

Measurement  of  the  Relative  Intensity  of  Different 
Radiations.  —  It  is  on  this  principle  that  rests  the  eye- 
estimation  of  temperatures,  such  as  are  made  by  workmen 
in  industrial  works.  Numerous  attempts,  none  very  suc- 
cessful, have  been  made  to  modify  this  method  and  make 
it  precise.  There  is  need  to  consider  this  only  from  the 
point  of  view  of  a  summary  control  over  the  heating  of 
industrial  furnaces. 

a.  Use  of  the  Eye.  —  Pouillet  made  a  comparison  of  the 
colors  of  incandescent  bodies  in  terms  of  the  air-thermom- 
eter. The  table  that  he  drew  up  is  reproduced  everywhere 
to-day: 


246  HIGH  TEMPERATURES. 

First  visible  red 525°        Dull  orange 1100° 

Dull  red 700          Bright  orange 1200 

Turning  to  cherry 800          White 1300 

Cherry  proper 900          Brilliant  white 1400 

Bright  cherry 1000          Dazzling  white 1500 

The  estimation  of  these  hues  is  very  arbitrary  and  varies 
from  one  person  to  another;  more  than  that,  it  varies  for 
the  same  person  with  the  exterior  lighting.  The  hues 
are  different  by  day  from  those  by  night;  it  is  thus  that 
the  gas-flame,  yellow  during  the  day,  appears  white  at 
night.  It  is  only  in  the  reds  that  any  accuracy  can  be 
had  by  the  eye-method.  Workmen  can  sometimes  guess  to 
better  than  25°  C.  up  to  800°  C.  At  1200°  errors  of  over 
200°  will  be  made. 

b.  Use  of  Cobalt  Glass.  —  One  may  exaggerate  the 
changes  of  hue  in  suppressing  from  the  spectrum  the 
central  radiations,  the  yellow  and  green  for  example,  so 
as  only  to  keep  the  red  and  the  blue.  The  relative  varia- 
tions of  two  hues  are  the  greater  the  more  separated  they 
are  in  the  spectrum;  now,  the  red  and  the  blue  form  the 
two  extremities  of  the  visible  spectrum. 

It  has  been  proposed  for  this  purpose  to  use  cobalt 
glass,  which  cuts  out  the  yellow  and  green,  but  lets  pass 
the  red  and  blue.  It  must  be  remembered  that  the  ratio 
of  the  radiations  transmitted  varies  with  the  thickness  of 
the  glass  as  well  as  with  their  absolute  intensities. 

Let  I a  and  /&  be  the  intensities  of  the  radiations  emitted, 
ka  and  kj,  the  proportions  transmitted  by  the  glass  through 
a  thickness  1.  Through  a  thickness  e  the  proportion 
transmitted  will  be 


which  will  vary  with  e  in  all  cases  that  fca  is  different 
from  fc. 


OPTICAL  PYROMETER.  247 

It  results  from  this  that  two  cobalt  glasses,  differing  in 
thickness  or  in  amount  of  cobalt,  will  not  give  the  same 
results.  So  that  if  the  cobalt  glass  habitually  used  is 
broken,  all  the  training  of  the  eye  goes  for  naught. 

Besides,  cobalt  has  the  inconvenience  of  having  an  insuf- 
ficient absorbing  power  for  the  red,  which  predominates 
at  the  more  ordinary  temperatures  that  we  make  use  of. 
It  would  be  possible,  without  doubt,  by  the  addition  of 
copper  oxide,  to  augment  the  absorbing  power  for  the  red. 

One  would  have  better  and  more  comparable  results  by 
employing  solutions  of  metallic  salts  or  of  organic  com- 
pounds suitably  chosen.  But  few  trials  have  been  made 
in  this  matter. 

Apparatus  of  Mesur6  and  Nouel. — It  is  known  that  by 
placing  between  two  nicols  a  plate  of  quartz  cut  perpen- 


FIG.  55. 

dicularly  to  the  axis  a  certain  number  of  the  radiations  of 
the  spectrum  are  suppressed.  This  latter  is  then  com- 
posed of  dark  bands  whose  spacing  depends  on  the  thick- 
ness of  the  quartz  and  the  position  of  the  angle  of  the 
nicols.  Mesure  and  Nouel  have  utilized  this  principle 
hi  order  to  cut  out  the  central  portions  of  the  spectrum; 
this  solution  is  excellent  and  preferable  to  the  use  of  absorb- 
ing media.  The  apparatus  (Fig.  55)  consists  essentially 
of  a  polarizer  P  and  an  analyzer  A,  whose  adjustment  to 


248  HIGH   TEMPERATURES. 

extinction  gives  the  zero  of  graduation  of  the  divided 
circle  CC.  This  circle  is  graduated  in  degrees  and  is 
movable  before  a  fixed  index  7.  Between  the  two  nicols 
P  and  A  is  a  quartz  Q  of  suitable  thickness,  carefully  cali- 
brated. The  mounting  M  allows  of  its  quick  removal 
if  it  is  necessary  to  verify  the  adjustment  of  the  nicols  P 
and  A.  The  quartz  Q  is  cut  perpendicularly  to  the 
axis.  A  lens  L  views  the  opposite  opening  C  furnished 
with  a  parallel-faced  plate  glass  or,  where  desired,  with 
a  diffusing-glass  very  slightly  ground. 

The  relative  proportions  of  various  rays  that  an  incan- 
descent body  emits  varying  with  the  temperature,  it  fol- 
lows that  for  a  given  position  of  the  analyzer  A  the  com- 
posite tint  obtained  is  different  for  different  temperatures. 

If  the  analyzer  is  turned  while  a  given  luminous  body 
is  viewed,  it  is  noticed  that  the  variations  of  colora- 
tion are  much  more  rapid  for  a  certain  position  of  the 
analyzer.  A  very  slight  rotation  changes  suddenly  the 
color  from  red  to  green.  Now,  if  the  analyzer  is  left  fixed, 
a  slight  variation  in  the  temperature  of  the  incandescent 
body  produces  the  same  effect.  The  transmission  hue  red- 
green  constitutes  what  is  called  the  sensitive  hue.  There 
are  then  two  absorptions,  one  in  the  yellow  and  the  other 
in  the  violet. 

This  apparatus  may  be  employed  in  two  different  ways. 
First  fix  permanently  the  analyzer  in  a  position  which  gives 
the  sensitive  hue  for  the  temperature  that  is  to  be  watched, 
and  observe  the  changes  of  hue  which  are  produced  when 
the  temperature  varies  in  one  direction  or  the  other  from 
the  chosen  temperature.  This  is  the  ordinary  method  of 
use  of  this  instrument.  It  is  desired  in  a  given  manu- 
facturing process  (steel,  glass)  to  make  sure  that  the  tem- 
perature of  the  furnace  rests  always  the  same;  the  instru- 
ment is  adjusted  once  for  all  for  this  temperature.  It 


OPTICAL  PYROMETER.  249 

suffices  to  have  but  a  short  experience  to  train  the  eye 
to  appreciate  the  direction  of  the  change  of  hue. 

The  inventors  have  sought  to  make  of  their  apparatus 
a  measuring  instrument;  this  idea  is  quite  open  to  de- 
bate. In  theory  this  is  easy;  it  suffices,  instead  of  hav- 
ing the  analyzer  fixed,  to  make  it  turn  just  to  the  securing 
of  the  sensitive  hue  and  to  note  the  angle  which  gives  the 
position  of  the  analyzer.  But  in  fact  the  sensitive  hue  is 
not  rigorously  determinate  and  varies  with  the  observer. 
A  graduation  made  by  one  observer  will  not  hold  for 
another.  It  is  not  even  certain  that  the  same  observer 
will  choose  always  the  same  sensitive  hue.  At  each  tem- 
perature the  sensitive  hue  is  slightly  different,  and  it  is 
impossible  to  remember  throughout  the  scale  of  tempera- 
tures the  hues  that  were  chosen  on  the  day  of  the  gradua- 
tion. There  is  even  considerable  difficulty  to  recall  this 
for  a  single  temperature. 

The  following  figures  will  give  an  idea  of  the  differences 
which  may  exist  between  two  observers  as  to  the  position 
of  the  sensitive  hue: 


Sun  ......................    6000°  84  86 

Gas-flame  .................    1680  65  70 

Red-hot  platinum  .........     800  40  45 

The  errors  in  the  estimation  of  temperatures  which 
result  from  the  uncertainty  of  the  sensitive  hue  will  thus 
exceed  100°.  With  observers  having  had  more  experience 
the  difference  will  be  somewhat  reduced,  but  it  will  re- 
main always  quite  large. 

Crova's  Pyrometer.  —  Crova  endeavored  to  give  to  the 
method  of  estimation  of  temperatures  based  on  the  un- 
equal variation  of  different  radiations  of  the  spectrum  a 


250  HIGH  TEMPERATURES. 

scientific  precision  by  measuring  the  absolute  intensity  of 
each  of  the  two  radiations  utilized ;  but  this  method,  from 
the  practical  point  of  view,  does  not  seem  to  ha ve-  given 
more  exact  results  than  the  preceding  ones. 

The  eye  is  much  less  sensitive  to  difference  of  intensity 
than  to  difference  of  hue,  so  that  there  is  no  advantage  in 
making  use  of  observations  of  intensity. 

Crova  compared  two  radiations, 

X  =  676  (red), 
^  =  523  (green), 

coming  from  the  object  studied  and  from  the  oil-lamp 
used  as  standard.  For  this  purpose,  by  means  of  a  vari- 
able diaphragm,  he  brings  to  equality  one  of  the  two  radia- 
tions emanating  from  each  of  the  sources,  and  measures 
afterwards  the  ratio  of  the  intensities  of  the  two  other 
radiations. 

The  apparatus  is  a  spectrophotometer.  Placed  before 
half  the  height  of  the  flame  is  a  total  reflecting  prism, 
which  reflects  the  light  from  a  ground  glass,  lighted  by  the 
radiations  from  an  oil-lamp,  having  first  passed  through 
two  nicols  and  a  diaphragm  of  variable  aperture.  On  the 
other  half  of  the  slit  is  projected  by  means  of  a  lens  the 
image  of  the  body  to  be  studied. 

Before  using  the  apparatus  it  is  necessary  to  adjust  the 
extreme  limits  of  the  displacement  of  the  spectrum  so  as 
to  project  successively  on  the  slit,  in  the  focus  of  the  eye- 
piece, the  two  radiations  selected  (,1  =  676  and  ,1  =  523). 
For  this  purpose  there  is  interposed  between  the  two 
crossed  nicols  a  4-mm.  quartz  plate  which  re-establishes 
the  illuminations;  for  extinction  again,  the  analyzer  must 
be  turned  115°  38'  for  ,1  =  523,  and  65°  52'  for  ,1  =  676. 
The  instrument  is  then  so  adjusted  that  the  dark  band 


OPTICAL  PYROMETER.  251 

produced  by  the  quartz  is  situated  in  the  middle  of  the 
ocular  slit. 

The  apparatus  thus  adjusted,  in  order  to  make  a  meas- 
urement at  low  temperatures,  inferior  to  those  of  carbon 
burning  in  the  standard  lamp,  one  brings  to  equality  the 
red  radiations  with  the  diaphragm,  then,  without  touching 
the  diaphragm  again,  the  green  is  brought  to  equality  by 
turning  the  nicol. 

The  optical  degree  is  given  by  the  formula 

N=  1000  cos2  a, 

denoting  by  a  the  angle  between  the  two  principal  sec- 
tions of  the  nicols. 

For  higher  temperatures  the  operation  is  reversed;  one 
brings  first  the  green  to  equality  by  means  of  the  dia- 
phragm, then  the  red  to  equality  by  a  rotation  of  the 
analyzer.  The  optical  degree  is  then  given  by  the  formula 

1000 

N = — o — ,  and  the  rotation  varying  from  0°  to  90°.  the 
cos2  a 

optical  degrees  vary  from  1000°  to  infinity. 

This  method,  which  is  theoretically  excellent,  possesses 
certain  practical  disadvantages: 

1.  Lack  of  precision  of  the  measurements.     In  admitting 
an  error  of  10  per  cent  in  each  one  of  the  observations 
relative  to  the  red  and  green  radiations,  the  total  possible 
error  is  20  per  cent;    now,  between  700°  and  1500°  the 
ratio  of  intensities  varies  from  1   to  5:    this  leads  to  a 
difference  of  &  in  800°,  or  32°. 

2.  Complication   and   slowness   of   observations.     It  is 
difficult  to  focus  exactly  on  the  body  or  the  point  on  the 
body  that  one  wishes  to  study.     The  set-up  and  the  tak- 
ing  of   observations   sometimes   require    about    half  an 
hour. 


252  HIGH   TEMPERATURES. 

3.  Absence  of  comparison  in  terms  of  the  gas-scale. 

The  a  priori  reason  that  had  led  to  the  study  of  this 
method  was  the  supposition  that,  in  general,  the  emissive 
power  of  substances  was  the  same  for  all  radiations  and 
that  consequently  its  influence  would  disappear  by  taking 
the  ratio  of  the  intensities  of  the  two  radiations.  The 
measurements  of  emissive  power  given  previously  prove 
that  this  hypothesis  is  the  more  often  inexact. 

Action  of  Light  on  Selenium. — It  has  been  known  for  a 
long  time  that  light  incident  upon  selenium  changes  the 
electric  resistance  of  the  latter,  and  pyrometers  based  on 
this  principle  have  been  devised.  Light  from  an  incan- 
descent source  whose  temperature  is  sought  falls  upon  a 
selenium  cell  forming  part  of  an  electric  circuit  in  which 
are  a  battery  and  ammeter.  As  the  light  varies  in  inten- 
sity due  to  changes  in  temperature,  the  resistance  of  the 
selenium  varies  and  the  indications  of  the  ammeter  may 
be  empirically  calibrated  in  terms  of  temperature.  As 
selenium  is  quite  insensible  to  the  invisible  heat-waves,  the 
lower  limit  of  this  method  is  above  incandescence.  Sele- 
nium also  requires  some  time  to  recover  its  original  resist- 
ance after  being  acted  upon  by  light,  and  this  lag  might 
prove  troublesome.  As  a  dial  instrument  is  used,  the 
method  could  readily  be  made  recording. 


CHAPTER  X. 
EXPANSION-  AND  CONTRACTION-PYROMETERS. 

Wedgwood's  pyrometer,  the  oldest  among  such  instru- 
ments, presents  to-day  hardly  more  than  an  historic 
interest,  for  its  use  has  been  almost  entirely  abandoned. 
It  utilizes  the  permanent  contraction  assumed  by  clayey 
matters  under  the  influence  of  high  temperature.  This 
contraction  is  variable  with  the  chemical  nature  of  the 
paste,  the  size  of  the  grains,  the  compactness  of  the  wet 
paste,  the  time  of  heating,  etc.  In  order  to  have  compa- 
rable results,  it  would  be  necessary  to  prepare  simultane- 
ously, under  the  same  conditions,  a  great  quantity  of  cylin- 
ders, whose  calibration  would  be  made  in  terms  of  the 
air-thermometer.  Wedgwood  employed  cylinders  of  fire- 
clay, baked  until  dehydrated,  or  to  600°;  this  preliminary 
baking  is  indispensable,  if  one  wishes  to  avoid  their  flying 
to  pieces  when  suddenly  submitted  to  the  action  of  fire. 
These  cylinders  have  a  plane  face  on  which  they  rest  in 
the  measuring  apparatus,  so  as  always  to  face  the  same  way 
(see  the  frontispiece).  The  contraction  is  measured  by 
means  of  a  gauge  formed  by  two  inclined  edges;  two 
similar  gauges  of  6  inches  in  length,  one  an  extension  of  the 
other,  are  placed  side  by  side;  at  one  end  they  have  a 
maximum  separation  of  0.5  inch,  and  at  the  other  a  mini- 
mum separation  of  0.3  inch.  Longitudinally  the  divisions 
are  of  0.05  inch;  each  division  equals  ^J^  of  f$  of  an  inch, 

253 


254  HIGH  TEMPERATURES. 

or  T^7  inch,  which  corresponds  to  a  relative  contraction 
of  T2iTrg.-i-15-5.=  g-Ljj.  in  terms  of  the  initial  dimensions. 

We  then  have  the  following  relation  between  the  Wedg- 
wood degrees  and  the  linear  contraction  per  unit  of  length : 

Wedgwood 0      30      60      90      120      150      180     210     240 

Contraction 0    0.05  0.10  0.15  0.20    0.25    0.30    0.35    0.40 

Le  Chatelier  has  made  experiments  to  determine  the 
degrees  of  the  Wedgwood  pyrometer  in  terms  of  the  scale 
of  the  air-thermometer  by  making  use  of  clayey  substances 
of  different  kinds,  and  in  the  first  place  of  the  cylinders 
from  an  old  Wedgwood  pyrometer  of  the  Ecole  des  Mines. 
The  contraction  which  accompanies  the  dehydration  is 
quite  variable  with  the  nature  of  the  pastes.  In  these 
experiments  the  time  of  heating  was  half  an  hour. 

Centigrade  temperature 600°  800°  1000°  1200°  1400°  1550° 

Wedgwood 0        4  15  36  90  132 

Argile  de  Mussidan 0        2  14  36  78  120 

Limoges  porcelain 0        0  2  21  88  91 

Faience  de  Choisy-le-Roi.  ...  02  5  12  48  75 

Faience  de  Nevers 0        0  0  32  Melted  Melted 

Kaolin 0        4  12  15  55  118 

Clay... .......  25)  0         4  9  19  123  160 

Titanic  acid. . .  75  ) 

This  table  shows  how  variable  are  the  observations;  it 
is  impossible,  consequently,  to  compare  the  old  measure- 
ments of  Wedgwood  and  of  his  successors,  because  the 
manufacture  of  the  cylinders  has  varied  with  the  course 
of  time. 

Wedgwood  had  given  a  graduation  made  by  a  process  of 
extrapolation  which  he  has  not  explained,  a  graduation 
according  to  which  he  attributed  10,000°  centigrade  to 
130°  of  his  pyrometer,  which  corresponds  to  about  1550°. 
One  might  still  seek  to  re-establish  the  graduation  by 
utilizing  the  determinations  of  the  fusing-points  of  the 


EXPANSION-  AND  CONTRACTION-PYROMETERS.  255 

metals  made  by  Wedgwood,  but  the  results  are  too  dis- 
cordant to  warrant  any  definite  conclusion.  According  to 
Wedgwood,  copper  would  be  more  fusible  than  silver,  iron 
would  not  be  far  removed  from  silver;  it  is  probable  that 
these  observations  were  made  with  very  impure  metals,  or 
at  any  rate  were  made  with  metals  much  oxidized  before 
their  fusion.  In  any  case  the  cylinders  which  he  made 
use  of  in  his  first  experiments  assume  a  much  greater  con- 
traction than  those  of  the  pyrometer  of  the  School  of 
Mines  whose  graduation  was  given  above.  One  might 
with  considerable  reserve  indicate'the  following  graduation 
for  measurements  made  with  the  first  cylinders  employed 
about  1780: 

Wedgwood  degrees 0  15  30  100          140 

Centigrade  degrees 600          800         1000         1200        1400 

The  preparation  of  the  cylinders  was  a  most  care-taking 
operation.  Moulded  in  soft  paste  they  were  necessarily 
somewhat  irregular.  After  the  first  baking  they  had  to 
be  trimmed  to  bring  them  to  a  uniform  size.  To-day,  in 
several  pottery  works  where  the  method  is  still  employed, 
a  much  greater  regularity  is  obtained  by  using  a  very  dry 
paste,  5  per  cent,  of  water  for  example,  moulding  it  under 
great  pressure,  about  100  kg.  per  square  centimeter,  in 
moulds  of  turned  steel.  The  precision  of  the  measurements 
is  increased  by  augumenting  the  diameter,  to  50  mm.  for 
example.  It  is  necessary  at  the  same  time  to  reduce  the 
thickness  to  about  5  mm.,  in  order  that  the  compression 
be  uniform  throughout  the  mass. 

This  apparatus  cannot  be  recommended  in  any  instance 
as  a  true  pyrometer,  serving  indirectly  to  evaluate  tempera- 
tures in  terms  of  the  air-thermometer  scale.  The  gradua- 
tion is  laborious  and  can  only  be  made  by  means  of  the 
intermediary  of  another  pyrometer;  the  use  of  fixed  points 


256 


HIGH  TEMPERATURES. 


is  not  adapted  for  this  graduation  because  the  curve  of 
contraction  of  clay  in  function  of  the  temperature  is  too 
irregular  for  two  or  three  points  to  determine  it;  in  no 
case  do  the  indications  of  this  instrument  possess  any  con- 
siderable precision. 

But  as  simple  pyroscope,  that  is  to  say,  as  an  apparatus 
to  indicate  merely  the  equality  or  inequality  of  two  tem- 
peratures, the  Wedgwood  pyrometer  is  very  convenient. 
It  has  the  advantage  of  costing 
almost  nothing  and  it  is  easy  to 
use  and  within  the  comprehension 
of  any  workman.  It  seems  to  be 
particularly  recommendable  for 
certain  ceramic  industries,  in 
which  the  ordinary  pastes  found 
there  .may  be  used  to  make  the 
contraction-cylinders.  It  is  neces- 
sary for  this  that  the  normal 
baking  of  these  pastes  is  stopped 
at  a  temperature  comprised  within 
the  period  of  rapid  contraction. 
This  is  the  case  with  fine  faience 
and  with  ordinary  earthenware. 

I  That  would  not  be  the  case,  how- 

ever, for  stannife  ous  faience  nor 
for  porcelain,  because  the  baking 
of  the  first  is  stopped  before  the 
beginning  of  the  contraction,  and 
that  of  the  second  after  its  finish. 
Expansion  of  Solids. — Some  of 
pIG  56.  the  earliest  forms  of   indicating- 

pyrometers   were   based   on   the 

relative  expansion  of  two  metals,  or  of  a  metal  and  graphite 
or  fire-clay.  Some  of  these  instruments  have  had  and  still 


EXPANSION-  AND  CONTRACTION-PYROMETERS.  257 

enjoy  a  very  wide  use  both  in  Europe  and  America,  and 
some  of  them  are  suitable  for  certain  industrial  processes 
not  requiring  exact  temperature  determination  or  control, 
as  air-blasts.  A  common  form  of  dial  instrument  is 
shown  in  Fig.  56.  A  tube  of  iron  encloses  a  rod  of  graphite, 
and  their  differential  expansion  with  change  in  tempera- 
ture is  communicated  by  levers  to  a  pointer  turning  over 
a  dial  graduated  in  degrees.  The  upper  limit  of  these 
instruments  is  about  800°  C.  (1500°  F.),  but  they  deteriorate 
rapidly  when  used  at  the  higher  temperatures.  Their 
indications  change  with  time  due  to  changes  produced 
in  the  materials  by  continued  heatings.  Correcting  the 
zero  of  such  an  instrument,  which  should  be  done 
frequently,  does  not  completely  correct  the  rest  of  the 
scale,  as  the  expansion  properties  of  the  two  materials 
change  differently  with  heating.  Varying  depths  of  im- 
mersion will  also  change  the  readings. 

The  Joly  Meldometer. — A  modified  form  of  this  instru- 
ment was  previously  mentioned,  p.  195.  As  in  its  usual 
form,  it  may  be  of  great  service  to  chemists,  metallurgists, 
and  others  in  determining  the  melting-points  and  identifi- 
cation of  minute  specimens  of  minerals,  salts,  metals, 
and  alloys,  a  further  description  may  be  of  interest. 

A  platinum  strip  (Fig.  57)  10  cm.  long,  4  mm.  wide, 
and  0.02  mm.  thick,  is  held  between  two  clamps  C,  C, 
and  kept  under  a  slight  tension  by  the  spring  s.  A 
storage-battery  current  controlled  by  a  small  step  rheostat 
R  is  sent  through  the  platinum  strip  whose  length  at 
any  instant  is  given  by  the  micrometer  screw  M ,  whose 
contact  is  made  appreciable  by  the  closing  of  the  circuit 
(f  an  electric  bell.  The  platinum  strip  is  calibrated 
preferably  by  means  of  salts  of  known  melting-points, 
as  KNO3  (399°  C.),  KBr  (723°),  and  K2SO4  (1071°). 
Metals  may  also  be  used,  but  they  tend  to  deteriorate 


258 


HIGH  TEMPERATURES. 


the  platinum.  The  upper  limit  of  the  instrument  is 
about  1500°  C.,  the  Pd  point  being  obtainable.  Per- 
manent elongation  sets  in  somewhat  before  this  point 


is  reached.  The  gold-point  (1065°  C.)  can  easily  be  de- 
termined to  better  than  2°  C.,  and  only  a  few  moments 
are  required  for  an  observation. 


EXPANSION-  AND  CONTRACTION-PYROMETERS.  259 

To  take  an  observation,  a  speck  of  the  specimen  whose 
melting-point  is  sought  is  placed  on  the  middle  of  the 
strip  under  a  low-power  microscope  magnifying  about 
twenty-five  times.  The  current  is  increased  and  at  the 
instant  of  melting,  as  observed  with  the  microscope,  the 
micrometer  is  set  to  make  contact  and  read,  when  by 
interpolation,  most  conveniently  made  graphically,  the 
temperature  is  found  corresponding  to  the  length  of  strip 
observed.  This  instrument  gives  a  nearly  but  not  quite 
linear  relation  between  length  of  strip  and  temperature. 

High-range  Thermometers. — Although  mercury  boils 
normally  at  about  356°  C.,  yet  this  liquid  subjected  to 
high  pressure  may  be  kept  from  boiling  and,  suitably 
enclosed,  may  be  used  as  thermometric  substance  to 
much  higher  temperatures.  Compressed  under  an  atmos- 
phere of  some  inert  gas,  as  nitrogen  or  carbonic  acid,  and 
enclosed  in  a  very  hard  glass,  as  Jena  59ra,  a  borosilicate 
glass,  the  mercury-thermometer  can  be  used  up  to  550°  C. 
(1000°  F.).  The  bulbs  of  such  thermometers  should  be 
carefully  annealed,  before  filling,  at  a  temperature  higher 
than  the  instrument  is  to  be  used,  and  the  thermometer 
should  also  be  annealed  after  it  is  made  and  allowed  to 
cool  slowly,  otherwise  considerable  and  irregular  changes 
in  its  indications  will  occur,  amounting  to  several  degrees. 
The  zero  reading  of  such  a  thermometer  should  be  taken 
after  every  observation  in  work  of  precision.  If  a  con- 
siderable length  of  stem  emerges  into  the  ah*  when  taking 
a  reading,  a  very  considerable  error,  25°  C.  or  so,  may  be 
introduced  at  high  temperatures  due  to  the  difference  in 
temperature  of  the  bulb  and  stem.  This  "  stem  correction" 
is  very  nearly: 

Stem  correction  =0.00016 -n-(T-t)°C., 


260  HIGH   TEMPERATURES. 

where  n  =  number  of  degrees  emergent  from  bath; 
T  =  temperature  of  bath; 

Z  =  mean    temperature   of    the   emergent    mercury 
column  determined  by  some  auxiliary  means, 
as  the  faden-ther  mo  meter  of  Mahlke.* 
The  glass  of  mercury-thermometers  has    been  success- 
fully replaced  by  quartz,  which  is  almost  an  ideal  ther- 
mometric  envelope,  possessing  an  insignificant  expansion 
and  no  appreciable  zero  lag,  and  capable  of  being:  used  at 
very  high  temperatures.    Such  mercury-in-quartz  thermom- 
eters are  now  constructed  by  Siebert  and  Kiihn,  and  are 
graduated  to  about  700°  C. 

Dufour  has  tried  to  substitute  tin  for  mercury-in-quartz 
thermometers,  thereby  attaining  a  temperature  of  over 
1000°  C.  Such  thermometers  have  not  yet,  however,  come 
into  use.  It  is  a  difficult  matter  not  yet  satisfactorily 
solved  to  find  a  substance  suitable  to  use  as  thermo- 
metric  fluid  in  quartz  at  high  temperatures. 

*  Mahlke,  Zeitsch.  /.  Instru'k.,  p.  58,  1893. 


CHAPTER  XI. 

FUSING-POINT,  DILUTION-,  AND  TRANSPIRATION- 
PYROMETERS. 

Fusing-point  Pyrometry. — A  long  time  ago  it  was  pro- 
posed to  compare  temperatures  by  means  of  the  fusing- 
points  of  certain  metals  and  alloys.  But  the  non-oxidiz- 
able  metals  are  not  numerous  and  all  are  relatively  very 
costly:  silver,  gold,  palladium,  platinum.  Use  has, 
however,  been  made  sometimes  of  these  metals  and  their 
alloys,  in  admitting  that  the  fusirig-point  of  a  mixture 
of  two  substances  is  the  arithmetical  mean  of  the  points 
of  fusion  of  the  components,  which  is  not  quite  exact. 
The  use  of  these  alloys  is  entirely  abandoned  to-day,  and 
with  reason. 

By  making  use  of  metallic  salts,  among  which  a  great 
number  may  be  heated  without  alteration,  one  might  con- 
stitute a  scale  of  fusing-points  whose  employ  would  be 
often  very  convenient;  but  this  work  is  not  yet  done,  at 
least  not  in  a  sufficiently  precise  manner.  To  the  separate 
salts  may  be  added  their  definite  combinations  and  their 
eutectic  mixtures  which  have  perfectly  definite  fusing- 
points.  But  one  cannot  take  any  mixture  whatever  of 
two  salts,  because  in  general  the  solidification  takes  place 
throughout  a  large  interval  of  temperature  and  in  a  pro- 
gressive manner. 

261 


262  HIGH  TEMPERATURES. 

Instead  of  utilizing  the  fusion  of  crystallized  substances 
which  pass  abruptly  from  the  solid  to  the  liquid  state,  use 
may  be  made  of  the  progressive  softening  of  vitreous 
matters,  that  is  to  say,  of  mixtures  containing  an  excess 
of  one  of  the  three  acids,  silicic,  boric,  or  phosphoric.  It 
is  necessary  in  this  case  to  have  a  definite  process  for 
defining  a  type  degree  of  softening;  a  definite  depression 
of  a  prism  of  given  size  is  taken.  These  small  prisms, 
formed  of  vitreous  matters,  are  known  under  the  name  of 
fusible  cones. 

This  method  was  first  devised  by  Lauth  and  Vogt,  who 
applied  it  in  the  manufactures  at  Sevres  before  1882. 
But  they  did  not  develop  it  as  far  as  was  possible;  they 
were  content  to  construct  a  small  number  of  fusible  cones 
corresponding  to  the  various  temperatures  employed  in  the 
manufacture  of  the  Sevres  porcelain. 

Seger's  Fusible  Cones. — Seger,  director  of  a  research 
laboratory  at  the  royal  pottery  works  of  Berlin,  published, 
in  1886,  an  important  memoir  on  this  question.  He  deter- 
mined a  whole  series  of  fusible  cones  of  intervals  of  about 
25°,  including  the  interval  of  temperature  from  600°  to 
1800°.  The  substances  which  enter  into  the  composition 
of  these  cones  are  essentially: 

Pure  quartz  sand; 

Norwegian  feldspar ; 

Pure  carbonate  of  lime;  ^ 

Zettlitz  kaolin. 

The  composition  of  this  last  is* 


SiO2 46.9 

A12O3 38.6 

FeO3 0.8 

Alkalies 1.1 

Water..,  .12.7 


FUSING-POINT  PYROMETERS. 


263 


In  order  to  obtain  very  infusible  cones,  calcined  alumina 
is  added,  and  for  very  fusible  cones  oxide  of  iron,  oxide  of 
lead,  carbonate  of  soda,  and  boric  acid. 

The  shape  of  these  cones  (Fig.  58)  is  that  of  triangular 
pyramids  of  15  mm.  on  a  side  and  50  mm.  high.  Under 
the  action  of  heat,  when  softening  begins,  they  at  first 
contract  without  change  of  form,  then  they  tip,  bending 
over,  letting  their  apex  turn  downwards,  and  finally  flatten- 


FIG.  58. 


ing  out  completely.  One  says  that  the  cone  has  fallen, 
or  that  it  has  melted,  when  it  is  bent  half-way  over,  the 
point  directed  downwards. 

The  fusing-points  of  these  substances  have  been  deter- 
mined at  the  Berlin  porcelain  works  by  comparison  with 
the  Le  Chatelier  thermoelectric  pyrometer,  previously  de- 
scribed. 

The  cones  are  numbered,  for  the  less  fusible,  which  were 
first  adjusted,  from  1  to  38;  this  latter,  the  least  fusible, 
corresponds  to  1980°.  The  second  series,  more  fusible, 
and  established  later,  is  numbered  from  01  to  022;  this 
last  cone,  the  most  fusible,  corresponds  to  590°. 

If,  instead  of  using  the  cones  of  German  make,  one 
wishes  to  make  them  himself  in  employing  the  same 
formulae,  it  is  prudent  to  make  a  new  graduation.  The 


264  HIGH  TEMPERATURES. 

kaolins  and  feldspars  from  different  sources  never  have 
exactly  the  same  compositions,  and  very  slight  variations 
in  their  amounts  of  contained  alkali  may  cause  marked 
changes  in  the  fusibility,  at  least  for  the  less  fusible  cones. 

It  is  to  be  noticed  that  in  a  great  number  of  cones  silica 
and  alumina  are  found  in  the  proportions  A12O3  +  10SiO2. 
This  is  for  the  reason  that  this  mixture  is  more  fusible 
than  can  be  had  with  silica  and  alumina  alone.  It  is  the 
starting-point  to  obtain  the  other  cones,  the  less  fusible 
by  the  addition  of  alumina,  and  the  more  fusible  by  the 
addition  of  alkaline  bases. 

The  table  on  pages  266  and  267  gives  the  list  of  cones 
of  Seger's  scale. 

These  cones  may  be  classed  in  a  series  of  groups  in  each 
of  which  the  compositions  of  different  cones  are  derived 
from  that  of  one  of  them,  generally  the  most  fusible,  by 
addition  in  varying  proportions  or  sometimes  by  substitu- 
tion of  another  substance. 

The  cones  28  to  38  are  derived  from  the  cone  27  by  the 
addition  of  increasing  quantities  of  A12O3. 

The  cones  5  to  28  from  the  cone  5  by  addition  of  in- 
creasing quantities  of  the  mixture  Al203+10Si02. 

The  cones  1  to  5  from  the  cone  1  by  substitution  of 
increasing  quantities  of  alumina  for  the  sesquioxide  of 
iron. 

The  cones  010  to  1  from  the  cone  1  by  the  substitution 
of  boric  acid  for  silica. 

The  cones  022  to  Oil  from  the  cone  022  by  the  addition 
of  increasing  quantities  of  the  mixture  Al2O3-f  2SiO2. 

Fig.  59  gives  the  graphical  representation  of  these  data; 
the  ordinates  are  temperatures,  and  the  abscissae  are  values 
of  x  from  the  table. 

These  fusible  cones  of  Seger  are  pretty  generally  used 
in  the  ceramic  industry;  they  are  very  convenient  in  all 


FUSING-POINT  PYROMETERS. 


265 


intermittent  furnaces  whose  temperature  has  to  increase 
constantly  up  to  a  certain  maximum,  at- which  point  the 
coohng-off  is  allowed  to  commence.  It  is  sufficient,  before 
firing  up,  to  place  a  certain  number  of  fusible  cones  oppo- 
site a  draft-hole  closed  by  a  glass,  through  which  they  may 


2000* 


SSfflffl 


FIG.  59. 


be  watched.  In  seeing  them  fall  successively,  one  knows 
at  what  moments  the  furnace  takes  on  a  series  of  definite 
temperatures. 

In  continuous  furnaces,  the  cones  may  be  put  into  the 
furnace  during  the  process,  but  that  is  more  delicate.     It 


266 


HIGH   TEMPERATURES. 


is  necessary  to  place  them  on  little  earthenware  supports 
that  are  moved  into  the  desired  part  of  the  furnace  by  an 
iron  rod.  When,  on  the  contrary,  they  are  put  in  place  at 
the  start  in  the  cold  furnace,  they  are  held  in  place  by  a 
small  lump  of  clay. 


Deg. 

Nos. 

T. 

Composition. 

X 

Formulas. 

38 

1890 

1A12O2+1    SiO2 

9 

36 

1850 

+  1.5  ' 

8 

35 

1830 

+  2      ' 

34 

1810 

+  2.5   ' 

33 
32 
31 
30 

1790 
1770 
1750 
1730 

+  3      ' 

+  4      ' 
+  5      * 
+  6      ' 

X  A1203 
+  (1-X)(A1203 
+  10  SiO2) 

29 

1710 

+  8      " 

28 

1690 

1            +10    " 

, 

27 

1670 

1  -j  JJ-3  gjO  [  +20(A1203  +  10  Si02) 

0 

26 

1650 

1        '  "           +7.2 

93 

25 

1630 

1          "           +6.6 

24 

1610 

+  6 

23 

1590 

+  5.4 

22 

1570 

+  4.9 

21 

1550 

+  4.4 

20 

1530 

+  3.9 

19 

1510 

+  3.5 

18 

1490 

+  3.1 

X(A1203+10  SiO2) 

17 

1470 

+  2.7 

4-fl      xi^'^      2*-H 

16 

1450 

+  2.4 

79 

\0.7  CaO  ' 

15 
14 

1430 
1410 

+  2.1 
+  1.8 

+  0.5(Al2O3+10  SiO2)) 

13 

1390 

+  1.6 

12 

1370 

+  1.4 

11 

1350 

+  1.2 

58 

10 

1330 

+  1 

9 

1310 

+  0.9 

8 

1290 

+  0.8 

7 

1270 

+  0.7 

6 

1250 

+  0.6 

5 

1230 

1          "           +0.5 

0 

4 

1210 

1          "           +0.5  Al2O3  +  4SiO2 

1 

3 

1190 

1          «•           _i_  J  0.45  A12O3  I    ,1  Q'O 
<  0.05  Fe2O3  1 

X  (0.5Al2O3  +  4  SiO2) 

2 

1170 

1          "           +|{J;J    Fe^3l+4Si°2 

+  (l-X).(0.5Fe2O 
+  4SiO2  +  0.7CaO) 

1 

1150 

1  0.2    Fe2O3  ' 

FUSING-POINT  PYROMETERS. 


267 


Nos. 

Deg. 

Composition. 

X 

Formula. 

01 
02 

1130 
1110 

,  (0.3K20) 
1"(0.7CaOf 

1 

<0.3A1203) 
•t(0.2Fe203f  + 

+            "          + 

(  3.95  SiO2 
j  3.90  SiO23 

1.05 

03 

1090 

1 

+            "          + 

J  3.S5  SiO2 

04 

1070 

1 

+            "          + 

j  3^80  SiO2 
1  0.20  BaOg 

XSiO 

05 

1050 

1 

+  1          "          + 

t  3.75  SiO2 
1  0.25  B-jOg 

1.25 

10 

06 

1030 

1 

+  1          "          + 

J  3.70  Si02 
1  0.30  B2O3 

V<«AW 

07 

1010 

1 

+  1          "          + 

j  3.65  SiO2 
I  0.35  BzOs 

+  <0.2Fe203,)+     fl°2, 

08 

990 

1 

+  1          "          + 

(  3.60  SiO2 
1  0.40  BzOa 

09 

970 

1 

+  1          "          + 

\  3.55  SiO2 

. 

010 

950 

1 

+  1          "          + 

\3.5   SiO2 

5 

Oil 

920 

1  1  o!5  PbO 

}  +0.8    Al2O3  + 

1  3.6  SiO2 
1  l.OBaOa 

0.61 

012 

890 

1 

+0.75     "     + 

I  3.5  SiO2 
1l.OB2O3 

013 

860 

1 

+0.70      "    + 

•j  j  '*  g^ 

014 

830 

1 

+0.65      "    + 

j3.3SiO2 

015 

800 

1 

+0.60      "    + 

j  s!2  SiO2 
(l.OBaOs 

0.57 

016 

770 

1         " 

+0.55      "    + 

j  3.1  SiO2 

X(2Si02+Ala03) 

017 

740 

1         " 

+0.50      "    + 

J  3.0  SiO2 
1l.OB2O3 

+d-x)(0;5PbO3[ 

018 

710 

1         " 

+0.40      "    + 

j  2.8  SiO2 

1  1  B209  f  / 

019 

680 

1 

+  0.30      "    + 

j  2.6  SiO2 

020 

650 

1         " 

0 
+  0.20      "    + 

J  2'.4  SiO2 
'  l.OBaOa 

021 

620 

1         " 

+0.10      "    + 

j  2.2  SiO2 
U.OBjjOs 

022 

590 

1 

+ 

{  2.0  SiO2 
ll.OB2O3 

0 

Wiborgh's  Thermophones. — Another  cheap,  discontin- 
ous  pyroscope  has  been  put  on  the  market  by  Wiborgh. 
His  thermophones  are  refractory  earth  cylinders  2.5  cm. 


268  HIGH 

long  and  2  cm.  in  diameter,  containing  an  explosive.  A 
thermophone  is  quickly  deposited  in  the  region  whose 
temperature  is  sought,  and  the  time  noted  to  the  fifth  of  a 
second  until  the  cylinder  bursts.  A  table  then  gives  the 
temperature.  Very  concordant  results  are  obtained  if 
the  thermophones  are  kept  dry,  different  cylinders  of  the 
same  set  agreeing  to  -J  sec,  or  20°  C.  at  1000°  C. 

Dilution-pyrometers. — If  a  current  of  liquid  or  gas  is 
kept  flowing  through  a  heated  space  it  is  evidently  possible 
to  estimate  the  temperature  of  the  latter  by  observing  the 
inlet  and  outlet  temperatures  of  the  fluid.  Carnelly  and 
Burton  constructed  such  a  pyrometer  using  water  flowing 
at  constant  head  from  a  tank  kept  at  constant  tempera- 
ture. The  graduation  of  such  a  pyrometer  is  purely  em- 
pirical and  may  be  effected,  for  a  given  heat  and  tempera- 
ture of  supply,  by  taking  the  inlet  and  outlet  temperatures 
for  three  or  more  known  temperatures  of  the  furnace.  For 
every  different  head  and  temperature  of  source  the  gradua- 
tion will  be  different.  Such  a  pyrometer  evidently  re- 
quires a  somewhat  cumbersome,  permanent  installation, 
and  has  the  further  disadvantages  of  not  being  direct- 
reading  and  having  its  indications  change  with  difficultly 
controllable  factors. 

For  determining  hot-blast  temperatures  air-dilution 
pyrometers  have  been  used,  air  from  the  outside  entering 
the  blast,  mixing  with  it,  and  the  temperature  of  the  out- 
coming  mixture  being  taken  with  a  mercury-thermometer, 
and  then  the  temperature  of  the  blast  computed  from  an 
empirical  calibration.  But  very  uncertain  results  can  be 
obtained  in  this  way,  as  they  will  depend  on  the  speed  of 
the  blast,  the  size  of  openings,  and  the  temperature  of 
the  diluting  air. 

Such  a  pyrometer  is  illustrated  in  Fig.  60. 

Transpiration-pyrometers.  --  Various    attempts    have 


T&ANSPI&A  TION-PYROMETERS. 


269 


been  made  to  construct  pyrometers  based  on  the  variation 
of  the  viscosity  of  gases  with  temperature,  and  this  sub- 
ject has  been  thoroughly  studied  by  Barus  and  by  Cal- 
lendar;  but  owing  to  the  complexity  of  the  viscosity- tem- 
perature relation  for  small  tubes,  no  simple  pyrometer 


FIG.  60. 

based  on  this  relation  alone,  not  requiring  an  arbitrary 
calibration,  has  been  devised. 

Job  has  shown  that  if  a  short  piece  of  platinum  wire 
be  inserted  in  the  end  of  a  porcelain  tube  of  less  than 
1  mm.  diameter  and  a  constant  current  of  gas,  as  from 
an  electrolytic  cell  or  blower,  be  passed  through  tliis 
capillary,  the  back  pressure  developed  will  be  proportional 
to  the  temperature,  or  T  =  k(H  —  h0),  where  H  is  given  by 
a  manometer  inserted  between  the  cell  or  blower  and 
the  porcelain  capillary,  and  h0  is  the  initial  pressure.  This 
simple  relation  holds  very  exactly  up  to  temperatures  as 


270  HIGH   TEMPERATURES. 

high  as  1500°  C.,  and  the  method  may  be  made  very  sensi- 
tive by  a  proper  choice  of  manometer  liquid  and  initial 
pressure  A0.  The  indications,  however,  vary  with  the  depth 
of  immersion  of  the  capillary,  and  they  depend  not  alone 
upon  the  viscosity  of  the  gas,  but  also  upon  the  relative 
expansion  of  platinum  and  porcelain. 

A  pyrometer  depending  upon  the  change  in  pressure 
produced  in  a  current  of  gas  or  vapor  passing  through  a 
small  orifice  at  high  temperature  has  been  developed  by 
Uhling  and  Steinbart,  using  a  steam- jet  aspirator  to  pro- 
duce a  steady  flow.  Although  simple  in  principle  the 
apparatus  as  constructed  is  very  complicated  and  costly. 
It  is  made  direct-reading  and  also  recording.  The  cali- 
bration is  empirical  and  the  apparatus  is  so  constructed 
that  temperatures  are  read  off  a  water-manometer  column. 
The  elaborateness  of  construction  of  such  a  pressure  appa- 
ratus renders  it  liable  to  deteriorate  with  time  and  use. 


CHAPTER  XIL 
RECORDING-PYROMETERS. 

AMONG  the  different  methods  for  the  measurement  of 
high  temperatures,  some  of  them  may  be  made  contin- 
uously recording.  This  recording  is  as  useful  for  industrial 
applications  as  for  scientific  investigations.  In  research 
laboratories  one  endeavors  as  much  as  possible  to  take 
observations  automatically,  escaping  the  influence  either 
of  preconceived  ideas  or  of  carelessness  of  the  observer;  in 
industrial  works  the  use  of  such  processes  gives  contin- 
uous control  over  the  work  of  the  artisans,  such  as  the 
presence  of  no  foreman  can  replace. 

The  record  may  be  made  by  means  of  a  pen  or  by 
photography.  The  former  of  these  methods,  more  simple 
to  handle,  is  preferable  in  works;  the  second,  whose  indi- 
cations are  more  precise,  is  preferable  in  the  laboratory. 
In  general,  however,  one  has  not  the  choice,  each  phenom- 
enon utilized  in  the  measurements  being  treatable  by 
only  one  method  of  registering.  So  far,  only  three  among 
the  different  pyrometers  have  been  rendered  recording: 

The  gas-thermometer  at  constant  volume; 

The  thermoelectric  pyrometer; 

The  electrical-resistance  pyrometer. 

But,  practically,  the  thermoelectric  pyrometer  has  been 
most  frequently  used  to  take  continuous  records. 

Recording  Gas-pyrometer. — The  transformation  of  the 
gas-thermometer  into  a  recording  instrument  is  extremely 

271 


272  jjIGH  TEMPEttATVRES. 

simple  and  has  been  long  since  effected.  It  suffices  to  join 
permanently  the  tube  from  the  porcelain  bulb  to  a  regis- 
tering-manometer to  realize  a  recording-pyrometer  theo- 
retically perfect.  But  practically  these  instruments  possess 
many  disadvantages  that  have  prevented  their  introduction 
generally. 

Above  1000°  the  permeability  of  the  porcelain  for 
water-vapor  is  sufficient  to  soon  render  them  useless. 
Investigations  made  by  the  Paris  Gas  Company  have  shown 
that  in  furnaces  heated  to  1100°  the  penetration  of  water- 
vapor  is  sufficiently  rapid  so  that  in  a  few  days  liquid 
water  collects  in  the  cold  parts  of  the  apparatus. 

Absolute  impermeability  of  the  apparatus,  which  is 
quite  indispensable,  since  its  operation  supposes  the  in- 
variability of  the  gaseous  mass,  is  very  difficult  to  obtain. 
Frequently  the  glazing  of  the  porcelain  has  holes  in  it. 
The  numerous  joints  entering  into  the  registering  appa- 
ratus, and  above  all  the  metallic  parts  of  the  apparatus, 
may  be  the  seats  of  very  small  leakages  difficult  to  locate. 

The  connection  of  the  metallic  parts  with  the  porcelain 
tube  is  generally  made  with  wax,  always  with  substances 
of  organic  origin  which,  in  the  vicinity  of  industrial  appa- 
ratus, generally  bulky  and  thick-walled,  cannot  be  pro- 
tected against  radiation  save  by  a  water-jacket.  This  is  a 
serious  inconvenience. 

In  laboratory  apparatus  of  small  size  the  protection  of 
the  joint  is  easier,  but  then  the  large  dimensions  of  the 
bulb,  as  has  been  indicated,  are  a  serious  disadvantage. 
One  cannot,  in  a  small  furnace,  find  a  large  volume  whose 
temperature  is  uniform. 

But  the  most  serious  disadvantage  of  the  recording  gas- 
pyrometer,  and  the  principal  reason  for  its  abandon- 
ment, is  the  difficulty  of  its  graduation.  Already  with 
the  mercury-manometer  the  waste  space  is  a  source 


KECORDING-PYROMETEtiS.  273 

of  complications.  However,  this  may  be  measured  and 
allowed  for.  With  the  registering-manometer  the  waste 
space  is  much  greater,  and  besides  variable  with  the 
deformation  of  the  elastic  tube.  Thus  the  graduation  can 
be  made  only  empirically,  employing  baths  of  fixed 
fusing-  or  boiling-points,  an  operation  almost  always  im- 
possible of  realization  with  an  apparatus  of  very  fragile 
porcelain. 

Electrical-resistance  Recording-pyrometer. — After  the 
gas-pyrometer,  the  oldest,  we  shall  describe  immediately 
the  electrical-resistance  pyrometer,  which  is  the  most 
recent. 

In  order  to  render  his  pyrometer  recording  (Fig.  61), 
Callendar  employs  the  following  very  simple  device:  Two 
of  the  branches  of  a  Wheatstone  bridge  used  to  measure 
the  resistance  of  the  heated  coil  are  made  of  a  single  wire, 
on  which  slides  a  rider  to  which  is  brought  one  of  the 
galvanometer  leads.  To  each  position  of  the  rider,  when 
the  galvanometer  is  at  zero,  corresponds  a  resistance,  and 
consequently  a  definite  temperature  of  the  coil.  The  posi- 
tion of  the  rider  may  be  easily  registered  by  attaching  to 
it  a  pen  writing  on  a  sheet  of  paper  which  moves  perpen- 
dicularly to  the  length  of  the  wire.  In  order  to  have  the 
curve  thus  obtained  correspond  to  that  of  temperatures,  it 
suffices  that  the  position  of  the  rider  be  at  each  instant  ad- 
justed so  as  to  keep  the  galvanometer  at  zero. 

This  result  is  obtained  by  means  of  a  clock-movement 
controlled  by  a  relay  that  the  galvanometer  works  in  one 
direction  or  the  other,  according  to  the  direction  of  the 
deflection  that  it  tends  to  take  on  from  the  zero-point. 
It  is  a  movable-coil  galvanometer  whose  needle  carries  an 
arm  which,  making  contact,  causes  a  current  to  pass. 

Fig.  62  gives  an  example  of  a  curve  recorded  by  this 
apparatus,  showing  the  effect  on  the  temperature  of  an 


274  HIGH   TEMPERATURES. 

annealing-oven  by  firing  by  an  old  hand  and  by  a  new 


one. 


FIG.  61. 

This  registering  apparatus  is  necessarily  very  costly, 
but  it  is  actually  the  only  sensitive  one  which  effects  the 
record  of  high  temperatures  by  purely  mechanical  means, 
without  the  intervention  of  photography ;  it  is  possible  that 


RECORDING-PYROMETERS. 


275 


276 


HIGH   TEMPERATURES. 


it  will  be  used  in  certain  large  industrial  works.  For  work 
in  the  laboratory  it  seems  less  convenient;  the  registering 
deprives  the  method  of  electrical  resistances  of  the  great 
precision  which  belongs  to  it  and  in -which  consists  its  great 
merit;  there  are  also  disadvantages,  such  as  the  necessity  to 
use  for  the  protection  of  the  coil  a  fragile  tube  of  porce- 
lain of  considerable  volume. 

'  This  recorder  possesses  an  interesting  detail  which 
assures  good  working  and  which  could  well  be  adopted  in 
other  similar  cases.  The  pointer  of  the  galvanometer- 
needle  does  not  hit  against  a  fixed  conductor,  to  which  it 
would  stick  on  account  of  heating  by  the  passage  of  the 
current  and  especially  the  extra  current  at  break.  This 
conductor  consists  of  the  metallic  circumference  of  a  wheel 
which  is  given  a  slow  constant  rotary  motion,  rendering  all 
adherence  impossible.  This  artifice  renders  possible  work- 
ing the  relays  by  means  of  a  sensitive  galvanometer,  which 
would  not  otherwise  be  realizable. 

Callendar  has  applied  the  same  method  of  recording  to 
Langley's  bolometer.  The  curve  of  Fig.  63  gives  the 
record  of  solar  radiation  for  a  day. 


i**~r^ 

rt~-^ 

/ 

J^ 

"V 

^"~"\ 

'X 

/ 

/ 

\ 

t 

\ 

.1 

V 

lr~ 

6        7        8        9        10      11    Noon    1234-56 
FIG.  63. 

The  same  method  of  recording  may  be  applied  to  the 
measurement  of  temperatures  by  means  of  thermoelectric 


RECORDING-PYROME  TERS.  277 

couples  by  using  the  method  of  opposition.  But  in  this 
case  the  strength  of  the  currents  available  to  work  the  re- 
lays is  much  more  feeble  than  in  the  preceding  applica- 
tions, so  that  a  great  sensibility  cannot  be  obtained. 
Fig.  61  shows  a  Callendar  recorder  as  made  by  the  Cam- 
bridge Instrument  Company,  arranged  for  the  thermo- 
electric measurement  of  temperatures  in  connection  with 
an  electric-resistance  furnace. 

Thermoelectric  Recording-pyrometer. — The  recording- 
pyrometers  most  currently  in  use  to-day  are  the  thermo- 
electric pyrometers  recording  photographically.  Numer- 
ous attempts  have  been  made  to  secure  a  recorder  with 
a  pen,  as  is  done  in  the  case  of  the  recording-voltmeters 
and  ammeters  hi  use  industrially,  but,  up  to  the  present, 
with  but  limited  success.  The  strengths  of  current  which 
can  be  utilized  are  very  weak;  for  a  precision  of  10°  an 
apparatus  sensible  to  4  O^TO  volt  is  necessary ;  the  resistance 
of  the  galvanometer-coils  should  be  considerable,  100 
ohms  at  least,  as  has  been  previously  explained,  and 
the  corresponding  current  will  be  only  a  millionth  of  an 
ampere.  There  are  on  the  market  such  alleged  recording- 
pyrometers,  but  they  are  for  the  most  part  constructed 
with  galvanometer-coils  of  but  few  ohms'  resistance  and 
cannot  give  measurements  of  temperature  exact  to  100°. 
Siemens  and  Halske  have  recently,  however,  produced 
a  recorder  (Fig.  64),  in  which  the  pen  touches  the  paper 
only  momentarily,  thereby  increasing  the  possibilities 
of  sensibility  to  that  of  a  good  millivoltmeter,  i.e.,  to  10° 
at  1000°  C. 

For  the  recording  of  temperatures  one  may  seek  two 
quite  different  results,  to  which  are  appropriate  two  meth- 
ods of  recording,  equally  different.  One  may  desire  to  deter- 
mine the  temperature  of  a  definite  epoch,  that  is  to  say, 
to  trace  the  temperature  curve  in  function  of  the  time. 


278  HIGH  TEMPERATURES. 

This  will  be  almost  always  the  object  in  view  in  industrial 
works.  It  suffices,  in  this  case,  to  let  fall  the  luminous 
beam  reflected  by  the  galvanometer-mirror  on  a  sensi- 
tive plate  possessing  a  vertical  movement  of  translation. 
The 'two  coordinates  of  the  curve  thus  recorded  give,  the 
one  temperature,  the  other  time.  One  may  desire,  on  the 
other  hand,  to  know  the  rate  of  variation  of  the  temper- 
ature at  a  given  instant,  and  at  the  same  time  the  cor- 


FIG.  64. 

responding  value  of  the  temperature.  This  is  the  case  in 
the  greater  number  of  laboratory  investigations  in  which 
is  desired  the  temperature  at  which  a  definite  phenomenon 
occurs:  fusion,  allotropic  transformation,  etc.;  and  in 
order  to  recognize  the  occurrence  of  this  phenomenon, 
use  is  ordinarily  made  of  the  accompanying  absorption  or 
liberation  of  latent  heat,  which  is  manifested  by  a  varia- 
tion in  the  law  of  heating  or  of  cooling. 

It  is  this  latter  method  of  recording  that  Le  Chatelier 
first  developed  during  his  investigations  on  clays.  A 
luminous  beam  reflected  by  the  galvanometer-mirror 
falls  periodically  at  regular  intervals,  of  a  second  for  in- 


RECORDING-PYROMETERS.  279 

stance,  upon  a  fixed  sensitive  plate.  The  distance  apart 
of  two  successive  images  gives  the  variation  of  temper- 
ature during  unit  time,  that  is,  the  rate  of  heating  or  of 
cooling;  the  distance  of  the  same  image  to  the  image  cor- 
responding to  the  beginning  of  the  heating  will  give  the 
measurement  of  the  temperature. 

In  all  cases  of  photographic  recording  it  is  necessary 
to  replace  the  ordinary  galvanometer-mirrors,  which  give 
images  quite  insufficient  as  to  definition  and  brightness, 
by  special  mirrors  made  of  a  plano-convex  lens,  silvered 
on  the  plane  surface.  These  mirrors  are  slightly  heavier 
than  parallel-face  mirrors,  but  have  two  important  ad- 
vantages: the  absence  of  extra  images  reflected  by  the 
front  surface  of  the  mirror,  and  a  greater  rigidity,  which 
obviates  accidental  bendings  of  the  mirror  arising  from 
the  attachments  to  its  support.  One  may  easily  get  good 
mirrors  of  this  type  of  20  mm.  diameter,  and  with  more 
difficulty  of  30  mm.  diameter.  These  last  give  nine  times 
more  light  than  the  mirrors  ordinarily  employed.  It  is 
easy  to  so  choose  the  lens  as  to  give  a  mirror  of  desired 
focal  length.  A  plano-convex  lens  whose  principal  focus 
by  transmission  is  1  m.  will  give,  after  silvering  the  plane 
surface,  an  optical  system  equivalent  to  a  spherical 
mirror  whose  radius  of  curvature  would  be  1  m. 

Discontinuous  Recording. — In  this  manner  of  recording, 
the  luminous  source  should  possess  periodic  variations; 
one  of  the  simplest  to  employ  is  the  electric  spark  between 
two  metallic  points.  The  interruption  of  the  current 
is  produced  by  a  pendulum  at  definite  intervals  of  time. 

In  order  to  have  a  spark  sufficiently  bright,  it  is  necessary 
to  use  an  induction-coil  so  worked  as  to  give  freely  sparks 
of  50  mm.,  and  to  reinforce  it  by  a  Ley  den  jar  which 
reduces  the  length  of  these  sparks  to  5  mm.;  it  suffices 
for  this  to  use  a  jar  of  1  to  2  liters.  The  choice  of  metals  for 


280 


HIGH    TEMPERATURES. 


the  points  is  equally  important;  zinc,  aluminium,  and 
especially  magnesium  give  sparks  that  are  very  photo- 
genic. These  metals  possess  the  disadvantage  of  ox- 
idizing quite  rapidly  in  the  air,  so  that  it  is  necessary  from 
time  to  time  to  clean  the  points  with  a  file.  The  metallic 
sticks  may  have  5  mm.  diameter,  and  the  distance  apart 
of  the  points  is  2  mm.  One  might  without  doubt,  using 
mercury,  which  gives  sparks  as  photogenic  as  does  mag- 
nesium, construct  an  enclosed  apparatus  in  which  the  metal 
would  be  preserved  unchanged. 

To  produce  the  interruption  there  is  attached  to  the 
pendulum  (Fig.  65)  a  vertical 
platinum  fork  which  dips  into  two 
cups  of  mercury  covered  with 
alcohol.  It  is  useful,  in  order  to 
reduce  to  a  minimum  the  resistance 
that  the  immersion  of  the  fork 
opposes  to  the  motion  of  the 
pendulum,  to  place  this  fork  in 
the  same  horizontal  plane  as  the 
axis  of  rotation  of  the  pendu- 
lum.  In  this  way  one  avoids 
the  translatory  movements  in  the 
mercury  which  cause  the  most 
trouble 

'  The  only  refinement  with  this  intermittent  lighting  is 
to  obtain,  with  a  spark  much  too  large  and  irregular  to  be 
photographed  directly,  the  illumination  of  a  very  narrow 
slit.  It  is  not  sufficient  to  place  the  spark  behind  the  slit 
and  at  a  small  distance  away,  because  the  slightest  dis- 
placement of  the  spark  would  cause  the  luminous  beam  to 
fall  outside  of  the  mirror  of  the  galvanometer.  This 
difficulty  is  overcome  by  a  well-known  artifice.  A  lens  is 
placed  between  the  electrodes  and  the  mirror  (Fig,  66); 


FIG-  65' 


RECORDING-PYROMETERS. 


281 


the  position  of  the  electrodes  is  so  adjusted  that  the  image 
of  the  mirror  is  formed  between  them.  With  a  distance 
apart  of  the  electrodes  of  2  mm.,  a  lens  of  100  mm.  focal 
length  and  a  mirror  of  25  mm.  diameter,  the  image  of  the 
latter  will  touch  the  two  points ;  the  spark  then  necessarily 
crosses  the  image  of  the  mirror,  and  the  radiations  passed 
by  the  lens  will  fall  certainly  upon  the  mirror.  One  is 
thus  sure  in  placing  before  the  lens  a  fine  metallic  slit 


I 


FIG.  66. 


that  all  the  rays  transmitted  will  reach  the  mirror  and 
will  be  sent  to  the  photographic  plate,  and  that  whatever 
may  be  the  position  of  the  slit  in  front  of  the  lens". 

To  save  time  it  is  advantageous  to  take  several  sets  of 
observations  on  the  same  plate;  this  is  easily  done  by 
arranging  the  plate  so  that  it  may  be  displaced  vertically 
between  two  series,  or  in  adjusting  the  slit  so  that  it  may 
be  moved  similarly  before  the  lens. 

The  diagram  (Fig,  67)  is  the  reproduction  of  negatives 
relative  to  the  action  of  heat  on  clays.  The  first  line  gives 
the  graduation  of  the  couple;  it  has  been  drawn  from 
several  different  photographs  which  have  been  grouped 
to  economize  space.  The  following  lines  are  reproductions 
of  negatives  made  photographically  without  any  inter- 
vention of  the  hand  of  the  engraver.  The  second  line, 
for  example,  represents  the  heating  of  an  ordinary  clay. 
A  slight  contraction  of  the  lines  between  150°  and  350° 
'indicates  a  first  phenomenon  with  absorption  of  heat; 


282  HIGH   TEMPERATURES. 

it  is  the  vaporization  of  the  enclosed  water.  A  second 
cooling  much  more  marked  between  550°  and  650°  shows 
the  dehydration,  properly  so  called,  of  the  clay,  the  libera- 
tion of  the  two  molecules  of  water  in  combination.  Finally, 
the  considerable  spacing  of  the  lines  at  1000°  shows  a 
sudden  setting-free  of  heat  corresponding  to  the  isomeric 
change  of  state,  after  which  the  alumina  becomes  in- 
soluble in  acids.  The  other  rows  refer  to  the  heating  of 


s  se  AU 

30°  100°  445°         665°          .        1045° 

t    Ml          niiiiiiiniiiiifiitiiwd  imiiiimiiHd  iiiiiiiiiiiiiiiiiiiiiiHiuiiwii  nn 


FIG.  67. 

other  varieties  of  clay,  the  third  row  to  kaolin,  the  fifth 
to  steargilite. 

Continuous  Recording. — The  continuous  recording  of 
temperatures  is  of  much  more  general  usage,  even  in 
scientific  laboratories,  by  reason  doubtless  of  the  greater 
simplicity  of  its  installation.  It  has  been  studied  especially 
by  Roberts-  Austen,  late  director  of  the  royal  mint  at  London. 
A  vertical  slit  lighted  from  a  convenient  source  projects 
its  image,  by  means  of  the  galvanometer-mirror,  on  a  me- 
tallic plate  pierced  by  a  fine  horizontal  slit,  and  behind  this 
slit  moves  a  sensitive  surface,  plate  or  paper,  which  receives 
the  luminous  beam,  defined  by  the  intersection  of  the 
horizontal  slit  with  the  image  of  the  vertical  slit.  If 
all  were  at  rest,  the  impression  produced  by  this  luminous 
beam  would  be  reduced  to  a  point.  If  the  plate  alone 
is  moved,  a  vertical  straight  line  will  be  had;  if  the  gal- 


RECORDING-PYROMETERS.  283 

vanometer-mirror  alone  turns,  a  horizontal  line.  Finally, 
the  simultaneous  displacement  of  the  plate  and  mirror 
gives  a  curve  whose  abscissae  represent  temperatures, 
and  whose  ordinates,  time.  The  illumination  of  the  slit  and 
the  motion  of  the  sensitive  surface  may  be  realized  in  many 
different  ways. 

Lighting  of  the  Slit. — There  are  two  quite  distinct  cases 
to  consider,  that  of  laboratory  researches  by  rapid  heating 
or  cooling,  which  last  only  a  few  minutes,  and  that  of 
continuous  recording  of  temperatures  in  industrial  works, 
which  may  last  hours  and  days,  that  is  to  say,  periods  100 
times  to  1000  times  longer.  The  rate  of  displacement  of 
the  sensitive  surface,  and  consequently  the  time  of  exposure 
to  the  luminous  action,  may  vary  in  the  same  ratio.  The 
luminous  source  necessary  will  be  therefore  quite  different, 
depending  upon  the  case.  For  very  slow  displacements 
it  is  sufficient  to  use  a  small  kerosene-lamp  with  a  flame 
of  5  to  10  mm.  high.  For  more  rapid  displacements 
use  may  be  made  of  an  ordinary  oil-lamp,  an  Auer  burner, 
o  an  incandescent  lamp ;  finally,  for  very  rapid  displace- 
ments of  the  sensitive  plate,  10  mm.  to  100  mm.  per  minute, 
one  may  advantageously  employ  the  oxyhydrogen  flame  or 
the  electric  arc.  For  oxyhydrogen  light  the  most  conve- 
nient is  the  lamp  of  Dr.  Roux,  with  magnesium  spheres;  it 
consumes  little  gas  and  is  enclosed  in  a  metallic  box  which 
prevents  all  troublesome  diffusions  of  the  light. 

The  electric  arc  gives  much  more  light  than  is  needed, 
and  the  rapid  wearing  away  of  the  carbon,  by  displacing 
the  positions  of  the  luminous  point,  renders  difficult  the 
permanence  of  suitable  illumination  of  the  slit.  For  very 
short  experiments  one  may  very  conveniently  use  the 
mercury-lamp  in  vacuo  (Fig.  68)  or  the  arc  playing  be- 
tween two  mercury  surfaces.  In  order  to  run  it,  3  amperes 
at  30  volts  are  requisite.  Its  only  disadvantage  is  to  go 


284 


HIGH   TEMPERATURES. 


•pIG 


out  after  running  a  few  minutes  on  account  of  the  evapo- 
ration of  the  mercury  in  the  central  tube.  It  suffices, 
it  is  true,  to  give  it  a  slight  jar  to  make 
it  go  again,  by  causing  a  small  quantity 
of  mercury  to  pass  from  the  outside 
annular  space  into  the  central  tube. 
Special  forms  of  mercury-lamp  exist,  how- 
ever, which  are  free  from  this  trouble. 

Whatever  the  luminous  source  em- 
ployed, the  slit  may  be  always  lighted  by 
means  of  a  lens  arranged  as  was  indicated 
I  K  for  discontinuous  recording,  that  is,  pro- 
\|/  _  jecting  upon  the  galvanometer-mirror  the 
-g  image  of  the  luminous  source.  When  this 
is  large  enough,  it  suffices  to  place  the 
slit  before  the  luminous  source,  bringing  it  up  close  enough 
so  as  to  be  sure  that  some  of  the  luminous  rays,  passing 
through,  fall  upon  the  mirror.  But  there  is  danger  here  of 
so  considerably  heating  the  slit  that  it  may  be  altered ;  for 
this  reason  one  is  led  to  use  more  voluminous  light-sources 
than  would  otherwise  be  necessary.  In  the  case  of  the  use 
of  a  lens,  the  useful  luminous  intensity  is  as  great  as  in 
placing  the  slit  immediately  next  to  the  luminous  source, 
so  long  as  the  image  of  the  latter  is  greater  than  the  gal- 
vanometer-mirror; now  with  the  ordinary  dimensions  of 
the  sources  employed  this  condition  is  always  fulfilled 
without  any  special  precaution. 

Instead  of  a  slit  lighted  by  a  distinct  luminous  source, 
use  may  be  made  of  a  platinum  wire,  or  better,  as  does 
Charpy,  employ  a  carbon  filament  of  an  incandescent  lamp 
heated  by  an  electric  current. 

In  order  that  the  line  traced  by  the  recorder  be  very 
fine,  it  is  necessary  that  the  two  slits,  the  luminous  slit  and 
the  horizontal  slit,  be  equally  fine.  Skilful  mechanicians 


H'ECORbiNG-PYRO:.!ETEttS. 

can  cut  such  slits  in  metals.  But  it  is  easier  to  make 
them  by  taking  a  photographic  plate  of  bromide-gelatine 
that  has  been  exposed  to  the  light,  developing  until  com- 
pletely black,  then  wash  and  dry.  By  cutting  the  gelatine 
with  the  point  of  a  penknife  guided  by  a  ruler,  one  may 
get  transparent  slits  of  a  perfect  fineness  and  sharp- 
ness. 

Sensitive  Surface. — For  sensitive  surfaces  use  is  made 
of  plates  or  films  of  bromide-gelatine.  Professor  Roberts- 
Austen  employed  exclusively  plates  which  permit  more 
easily  the  printing  of  a  great  number  of  positive  proofs. 
Charpy,  in  his  researches  on  the  tempering  of  steel,  made 
use  of  sensitive  paper,  which  permits  a  much  more  simple 
installation. 

Paper. — For  industrial  recording,  paper  would  allow  of 
the  employing  large  rolls  lasting  several  days,  as  in  the 
recording  magnetic  apparatus  of  Mascart.  But  in  general 
one  wants  to  have  quickly  the  results  of  the  record;  this 
is  always  the  case  in  laboratory  investigations,  and  almost 
always  in  industrial  studies.  It  is  thus  preferable  to  be 
content  with  quite  short  bands  of  paper  rolled  on  a  cyl- 
inder. There  exists  such  a  model  quite  well  known  and 
easy  to  use :  the  recording-cylinders  with  an  interior  clock- 
movement  of  the  firm  Richard,  Paris.  They  may  be 
ordered  from  the  maker  with  any  desired  rate  of  rotation  ; 
unfortunately  this  rate  cannot  be  changed  at  the  pleasure 
of  the  operator,  a  desideratum  in  laboratory  investiga- 
tions. 

Fig.  69  represents  the  installation  of  the  recording- 
pyrometer  used  by  Charpy  in  his  researches  on  the  tem- 
pering of  steel.  To  the  right  is  the  galvanometer,  to  the 
left  the  Richard  recording-cylinder,  and  in  the  middle 
the  electric  furnace  used  for  heating  the  samples  of 
steel. 


286' 


HIGH  TEMPERATURES. 


Plates. — The  plate  may  be  placed  in  a  movable  frame 
regulated  by  a  clock-movement;   this  is  the  first  arrange- 


FIG.  70. 


ment  employed  by  Prof.  Roberts- Austen  (Fig.  70).  But 
this  installation,  somewhat  costly  and  complicated,  has  the 
same  disadvantage  as  the  recording-cylinders  in  that  but 


RECORDING-PYROMETERS. 


287 


a  single  speed  can  be  given  to  the  sensitive  surface.  In 
order  to  drive  the  plate,  Roberts- 
Austen  later  used  a  buoyed  sys- 
tem in  which  the  rate  of  rise  of 
level  of  the  water  is  controlled 
at  will  by  the  agency  of  a  Ma-  1*  l[ 

riotte's  flask  and  a  simple  water- 
cock.  The  plate  is  kept  in  an 
invariable  vertical  plane  by  means 
of  two  lateral  cleats  whose  fric- 
tion is  negligible  on  account  of 

the  mobility  of  the  float.     The  .. .. 

sketch  (Fig.  71)  gives  the  arrange-  FIG.  71. 

ment  of  a  similar  apparatus  made 

by  Pellin  for  the  laboratory  of  the  College  de  France. 
It  carries  a  13X18  cm.  plate  which  is  attached  to  the 
float  by  means  of  two  lateral  springs  not  shown  in  the 
sketch.  Neither  are  the  two  guides  of  the  float,  immersed 
in  water,  indicated;  the  play  next  the  cleats  is  only  two 
tenths  of  a  millimeter.  The  uncertainty  that  this  play 
can  cause  in  the  position  of  the  plate  is  quite  negligible. 
The  curve  (Fig.  72)  is  the  reproduction  of  an  experiment 
made  with  such  an  arrangement  by  Roberts-Austen  on 
the  solidification  of  gold. 

During  the  whole  period  of  freezing,  the  temperature 
remained  stationary,  then  lowering  of  temperature  was 
produced  at  a  regularly  decreasing  rate  as  the  temperature 
of  the  metal  approached  that  of  the  surroundings. 

It  is  indispensable  to  trace  on  each  sensitive  surface  on 
which  is  to  be  recorded  a  curve,  the  line  corresponding  to 
the  surrounding  temperature,  or  at  least  a  parallel  refer- 
ence line.  This  is  very  easy  in  the  case  of  the  guided 
plate  or  of  the  paper  rolled  on  a  cylinder.  It  suffices, 
after  having  brought  the  couple  to  the  temperature  of  its 


288  HIGH   TEMPERATURES. 

surroundings,  to  displace  in  the  opposite  direction  the 
sensitive  surface;  the  second  curve  traced  during  this 
inverse  movement  is  precisely  the  line  of  the  zero  of  the 
graduation  of  the  temperatures.  But  this  is  a  dependence 
that  may  be  evaded  by  registering  at  the  same  time  as  the 
curve  a  reference  line  by  means  of  a  fixed  mirror  attached 
to  the  galvanometer  in  the  path  of  the  luminous  beam 
which  lights  the  movable  mirror.  Roberts-Austen  like- 


1065°  C. 


FIG.  72. 

wise  makes  use  of  the  luminous  beam  reflected  by  the  fixed 
mirror  to  inscribe  the  time  in  a  precise  manner.  A 
movable  screen  driven  by  a  second  pendulum  cuts  off  at 
equal  intervals  of  time  this  second  luminous  beam.  The 
reference  line,  instead  of  being  continuous,  is  made  up  of 
a  series  of  discontinuous  marks  whose  successively  corre- 
sponding parts  are  at  intervals  of  one  second  as  is  shown 
in  Fig.  72. 

The  curves  once  obtained  must  be  very  carefully  ex- 
amined to  recognize  the  points  where  the  gradient  pre- 
sents slight  anomalies,  characteristic  of  the  transforma- 


RECORDING-PYROMETERS.  289 

tions  of  the  body  studied.  Generally  these  irregularities 
are  very  insignificant,  and  it  would  be  well,  in  order  to 
recognize  them  with  certainty,  to  obtain  curves  traced  on 
a  much  greater  scale.  Practically  this  magnification  is 
not  possible  without  auxiliary  devices  which  limit  either 
the  range  or  the  sensibility;  thus  the  sensitiveness  of  the 
galvanometer  may  be  increased,  and  thus  the  deflection, 
but  then  for  the  greater  range  of  temperature  the  luminous 
image  would  fall  off  the  sensitive  plate.  Prof.  Roberts- 
Austen  has  overcome  this  difficulty  in  an  ingenious  man- 
ner. He  no  longer  registers  the  temperature  of  the  body, 
but  the  difference  between  this  temperature  and  that  of 
a  neighboring  body  which  presents  no  transformation, 
platinum  for  instance.  This  difference  of  temperature, 
always  small,  may  be  recorded  by  a  very  sensitive  gal- 
vanometer. If,  at  a  given  moment,  the  body,  other 
than  the  platinum,  undergoes  a  change  of  state  accom- 
panied by  even  very  weak  heat  phenomena,  the  difference 
of  the  two  temperatures,  by  reason  of  its  small  value, 
will  undergo  variations  relatively  very  great.  If  it  is 
desired  not  merely  to  recognize  the  existence  of  a  phenom- 


enon, but  besides  to  measure  the  temperature  at  which 
it  is  produced,  it  is  necessary  to  employ  simultaneously 


290 


HIGH  TEMPERATURES. 


a  couple  connected  to  another  galvanometer.  With  three 
leads,  two  of  platinum  and  one  of  platinum-rhodium,  a 
complex  couple  may  be  made,  giving  simultaneously  the 
actual  temperatures  and  the  differences  of  temperature 
of  two  neighboring  bodies.  The  diagram  (Fig.  73)  gives 


„    FIG.  74. 

an  idea  of  this  arrangement  which  has  proved  very  use- 
ful in  the  hands  of  Roberts- Austen  for  the  study  of  alloys, 
and  particularly  for  the  study  of  the  transformations  of 
irons  and  steels.  The  curve  of  the  solidification  of  tin 
is  reproduced  in  Fig  74,  as  obtained  by  this  method. 
The  double  inflection  indicates  the  existence  of  marked 
under-cooling;  the  tin,  before  freezing,  is  lowered  to  2° 
below  its  fusing-point,  to  which  it  returns  suddenly  as 
soon  as  solidification  sets  in. 

Recording  pyrometers  have  been  for  the  most  part  em- 
ployed up  to  the  present  only  in  scientific  laboratories. 
There  exist,  however,  a  few  in  metallurgical  works,  as  the 


RECORDING-PYROMETERS. 


291 


blast-furnaces  at  Clarence  Works  of  Sir  Lothian  Bell,  the 
blast-furnaces  of  Dowlais  and  in  the  Creusot  steel-works. 
The  curves  of  Fig.  75  give  an  example  of  the  curves 
obtained  at  Clarence  Works;  the  lower  curve  gives  the 


800°C. 


600' 


400  °C. 


1 

1 

r 

\% 

S 
i 

"\ 

t 

'"' 

x 

x; 

i 

/^ 

1 

.500° 


\ 


A 


\ 


FIG.  75. 


temperature  of  the  gas  at  the  furnace-mouth,  and  the 
upper  curve  that  of  the  hot  blast. 

Modifications  of  Sir  Roberts- Austen' s  Recorder. — The 
principal  source  of  trouble  with  the  autographic  appa- 
ratus of  Sir  Roberts-Austen  is  the  difficulty  in  giving  a 
uniform  steady  motion  to  the  photographic  plate  and 
also  the  necessity  of  additional  graphical  construction 
when  phenomena  involving  differences  of  temperature 
are  studied,  as  the  critical  points  of  steels. 

Mr.  Saladin  of  the  Creusot  Works  and  also  Prof.  Le 
Chatelier  have  devised  a  method  which  permits  the 
photographic  plate  to  remain  fixed  in  position  and  in 
so  placing  the  two  galvanometers  as  to  cause  the  lumi- 


292 


HIGH   TEMPERATURES. 


nous  beam  reflected  by  one  mirror  to  be  deflected  horizon- 
tally, while  the  beam  reflected  by  the  other  mirror  is 


Pt.— Kh. 


FIG.  76. 


deflected  vertically.  It  is  an  application  of  the  principle 
of  Lissajoux.  The  arrangement  of  the  apparatus  is  as 
shown  in  Fig.  76. 


RECORDING-PYROMETERS.  293 

Light  from  the  source  S  (Fig.  76),  an  acetylene  flame 
for  instance,  strikes  the  mirror — here  a  right-angled 
prism,  to  give  better  definition — of  the  sensitive  gal- 
vanometer Glf  whose  deflections  measure  the  differences 
in  temperature  between  the  piece  of  steel  or  other  object 
whose  critical  points  are  under  observation  and  the 
comparison  block,  which  may  be  platinum,  quartz,  or 
a  25  per  cent  nickel  steel  which  has  no  critical  point 
above  0°  C. 

The  horizontal  deflections  of  the  beam  of  light  are 
now  turned  into  a  vertical  plane  by  passing  through  the 
totally  reflecting  prism  placed  as  shown  at  M. 

A  second  galvanometer,  whose  deflections  are  a  measure 
of  the  temperature  of  the  sample  and  whose  mirror  is 
at  right  angles  to  the  first,  reflects  the  incident  beam 
horizontally  which  is  focussed  by  the  lens  L,  upon  the 
ground-glass  screen  or  photographic  plate  at  P.  The 
spot  of  light  has  thus  impressed  upon  it  two  motions  at 
right  angles  to  each  other,  giving,  therefore,  a  curve 
whose  abscissae  are  proportional  to  the  temperature  of 
the  sample,  or  more  strictly  to  the  E.M.F.  's  generated  by 
the  thermoelectric  couple,  and  whose  ordinates  are  pro- 
portional to  the  differences  in  temperature  between  the 
sample  and  the  comparison  block.  At  the  beginning  of 
each  experiment,  if  a  permanent  record  is  desired,  two 
axes  are  traced  on  the  photographic  plate  by  a  slight 
deviation  of  the  galvanometer-mirrors,  and  this  can 
readily  be  produced  by  sending  through  them  successively 
two  currents  of  equal  intensity,  but  of  opposite  direction, 
using  a  commutator  C  for  this  purpose. 

In  Saladin's  apparatus  the  two  galvanometers  are  each 
at  a  conjugate  focus  of  a  lens  L,  but  in  Le  Chatelier's 
form  the  galvanometers  are  brought  close  together  and 
the  lens  L  omitted,  forming  a  compact  apparatus  mounted 


294  HIGH   TEMPERATURES. 

in  a  small  portable  case  having  a  glass  front  which  carries 
the  two  lenses  required  for  the  projection. 

The  sensitiveness  of  the  method  depends  upon  the 
sensitiveness  of  the  galvanometer  Glt  which  may  be  readily 
made  to  give  five  or  six  millimeters  for  each  degree  centi- 
grade. 


CHAPTER  XIII. 
STANDARDIZATION  OF  PYROMETERS. 

Fixed  Points. — As  the  scale  determined  by  the  gas- 
thermometer  is  the  one  universally  recognized,  it  is  neces- 
sary in  order  to  graduate  a  pyrometer,  to  express  its  indi- 
cations in  terms  of  the  gas-scale.  In  general  it  is  not 
feasible  to  compare  the  readings  of  a  pyrometer  directly 
with  those  of  the  gas-thermometer.  The  use  of  the  latter 
becomes  restricted  mainly  to  the  establishment  of  certain 
constant  reproducible  temperatures  or  fixed  points  such 
as  are  given  by  freezing-points  and  boiling-points  of  the 
chemical  elements  and  of  certain  compounds.  The  ac- 
curacy attainable  in  pyrometric  researches  is,  therefore, 
limited  by  the  exactness  of  our  knowledge  of  these  refer- 
ence temperatures,  and  their  determination  has  been  and 
still  is  of  the  most  fundamental  importance  in  pyrometry. 
There  have  been  a  great  many  temperatures  suggested 
for  this  use,  but  the  actual  number  available  is  very  small. 
Preference  should  be  given  to  those  determinations  made 
with  the  gas-thermometer,  although  there  are  others 
made  indirectly  in  terms  of  the  gas-scale,  as  with  thermo- 
couples and  resistance-thermometers,  which  are  of  con- 
siderable weight. 

We  have  already  called  attention  to  many  of  these  de- 
terminations, among  which  the  following  are  to  be  con* 
sidered: 

295 


296  HIGH  TEMPERATURES. 

Sulphur. — (Boiling)  444°.6  C.  under  a  pressure  of  760 
mm.  with  a  variation  of  0°.095  per  millimeter  change  of 
mercury  in  the  atmospheric  pressure. 

The  boiling-point  of  sulphur  has  been  the  object  of 
several  series  of  distinct  observations,  among  which  we 
may  cite: 

Regnault 448° 

Crafts 445 

Callendar  and  Griffiths 444  . 5 

Chappuis  and  Barker 444  . 7 

Rothe 444  .7 

Regnault 's  figure  was  obtained  by  plunging  the  reser- 
voir of  the  thermometer  in  the  liquid  sulphur;  but  this 
liquid  will  superheat,  and  so  gives  too  high  a  value.  The 
other  three  very  concordant  results  were  obtained  in  the 
vapor.  The  sulphur-point  is  easy  to  get  experimentally 
if  care  is  taken  to  guard  against  superheating  and  if  a 
considerable  volume  is  used  •  fom'mercial  sulphur  is  suffi- 
ciently pure  for  this  purpose.  Electrical  heating  can  be 
used  to  advantage,  which  is  also  true  for  the  establish- 
ment of  the  other  fixed  points. 

The  result  first  published  by  Chappuis  and  Harker, 
using  a  constant-volume  thermometer,  was  445.2,  but  this 
difference  from  Callendar  and  Griffiths'  result  was  shown 
probably  to  be  mainly  due  to  an  incorrect  value  assumed 
for  the  expansion  coefficient  of  the  porcelain  bulbs  used 
by  the  former. 

Callendar  and  Griffiths  worked  with  a  constant-pressure 
thermometer  and  it  is  of  interest  to  note  that  the  out- 
standing difference  between  the  two  most  reliable  ex- 
perimental determinations  by  the  constant-volume  and 
constant-pressure  methods  is  of  the  order  of  difference 
between  the  two  gas-scales — constant  volume  and  con- 


STANDARDIZATION  OF  PYROMETERS.          297 

slant  pressure — as  seen  from  Callendar's  table  (p.  32). 
In  fact,  in  work  of  the  highest  precision  it  will  probably 
soon  be  necessary  to  reduce  observations  to  the  thermo- 
dynamic  scale. 

Zinc. — (Freezing)  419°.0  C.  Freezing-points  undergo  un- 
appreciable  changes  with  variations  in  atmospheric  pres- 
sure and  their  experimental  determination  is  somewhat 
easier  than  for  boiling-points  if  a  thermocouple  is  used. 
The  direct  determination  of  a  metallic  freezing-  or  melting- 
point  with  a  gas-thermometer  is  beset  with  almost  insur- 
mountable experimental  difficulties,  so  recourse  is  always 
had  to  some  auxiliary  pyrometer  whose  indications  have 
been  exactly  calibrated  by  direct  comparison  with  a  gas- 
thermometer. 

Zinc  is  easily  gotten  in  sufficient  purity.  Some  recent 
determinations  of  this  point  are: 

Heycock  and  Neville 419° .  0  C. 

Stansfield 418  .2 

Holborn  and  Day 419  .0 

The  method  employed  by  Stansfield,  recording  thermo- 
couple, was  not  as  reliable  as  those  of  the  other  two,  the 
first  of  whom  used  a  platinum  resistance  thermometer 
calibrated  at  the  points  0°,  100°,  and  444°.53,  and  the  last, 
Holborn  and  Day,  thermocouples  compared  directly  with 
their  constant-volume  nitrogen-platinum-bulb  thermom- 
eter. 

Zinc. — (Boiling)  920°  C.  with  a  variation  of  0°.15  for 
a  change  of  1  mm.  in  the  atmospheric  pressure. 

The  boiling-point  of  zinc  has  been  the  object  of  prob- 
ably more  determinations  than  any  other,  and  yet  it  is 
the  least  best  known  and  consequently  the  most  unre- 
liable to  try  and  use,  and  is  not  to  be  recommended.  It 
has  been  the  object  of  so  much  study,  undoubtedly,  as 


298  HIGH   TEMPERATURES. 

it  was  apparently  the  one  point  near  the  upper  limit  of 
the  gas-thermometer  which  could  be  determined  directly 
by  this  instrument,  but  superheating  effects  in  vapors  at 
such  high  temperatures  and  an  even  temperature  distri- 
bution are  very  difficult  to  obtain  even  with  electrical 
heating. 

Some  of  the  results  obtained  are  shown  by  the  following 
table: 

E.  Becquerel 930°  and 890°C. 

Sainte-Claire-Deville 915    to    945 

Barus 926  and  931 

Violle 930 

Holborn  and  Day 910    to    930 

Callendar 916 

.    •    D.  Berthelot 918 

The  value  930°  as  given  by  Violle's  and  Barus '  results 
was  generally  accepted  until  recently,  but  the  more  recent 
determinations  indicate  930  to  be  over  10°  high.  The 
value  adopted,  920°,  is  probably  not  in  error  by  over  5°  C. 

Gold.— (Fusion  or  Freezing)  1065°  C.  This  point  is  to- 
day one  of  the  best-known  fixed  points,  and  gold  pos- 
sesses the  advantages  of  being  obtainable  in  very  great 
purity,  is  not  oxidizable  in  air,  nor  is  it  readily  attacked 
by  the  silicious  materials  used  in  crucibles,  etc.  Its  cost 
is  its  only  drawback  for  use  in  considerable  quantities, 
but  methods  have  been  devised,  as  inserting  a  short  length 
of  wire  between  the  leads  of  a  thermocouple,  requiring 
only  very  minute  amounts  of  gold.  These  wire  methods 
give  the  same  results  as  the  crucible  method,  as  shown  by 
Holborn  and  Day  and  by  D.  Berthelot. 

The  early  determinations  of  the  gold-point  were  quite 
discordant,  but  the  later  ones  where  electric  heating  was 
employed  are  in  excellent  agreement. 


STANDARDIZATION  OF  PYROMETERS.          299 

Pouillet 1180°  C. 

E.  Becquerel 1092   and  1037 

Violle 1045 

Holborn  and  Wien 1070    to    1075 

Heycock  and  Neville 1062 

D.  Berthelot 1064 

Holborn  and  Day 1064 

Jacquerod  and  Perrot 1067 

Violle 's  value  was  long  quoted  as  the  best  for  the  gold- 
point,  but  the  later  determinations  show  it  to  be  20°  low. 
Holborn  and  Wien's  high  value  was  obtained  with  a 
porcelain-bulb  thermometer  and  is  to  be  considered  as 
replaced  by  Holborn  and  Day's  value,  to  obtain  which 
nitrogen  in  a  Pt-Ir  bulb  was  used,  together  with  a  thermo- 
couple. The  agreement  of  their  results  when  working 
under  various  conditions  is  shown  from  the  following 
observations : 

Gold,  sample  1 1064. 0±0. 6  (crucible  method) 

2 1063.5 

"        2 1063.9  (wire  method) 

Not  less  than  300  grammes  was  used  for  observations 
in  both  graphite  and  porcelain  crucibles,  while  by  the 
wire  method  0.03  gramme  of  the  metal  suffices. 

Berthelot  used  his  optical  gas-pyrometer  in  connection 
with  thermocouples  and  considers  his  result  to  be  in  error 
by  less  than  2°.  Heycock  and  Neville's  result  was  ob- 
tained by  extrapolation  above  the  sulphur-point  of  the 
platinum  resistance  formula,  while  Jacquerod  and  Perrot 's 
value  was  obtained  in  terms  of  a  quartz-bulb  constant- 
volume  thermometer  filled  with  various  gases,  the  results 
agreeing  to  a  few  tenths  of  a  degree.  They  used  a  modified 
form  of  the  wire  method,  which  consisted  in  making  a 
small  piece  of  gold  wire  a  part  of  an  alternating  electric 


300  HIGH   TEMPERATURES. 

circuit,  melting  of  the  gold  being  noted  by  cessation  of 
sound  in  a  telephone. 

Berthelot  has  called  attention  to  the  fact  that  these 
later  determinations  are  sufficiently  concordant  to  warrant 
reducing  them  to  the  thermodynamic  scale  (see  p.  33). 


Observer.  Ga,  Correction, 


D.  Berthelot.  .  .  . 

Air 

76 

cm 

+  1° 

.360. 

1064 

1065 

.6 

Holborn  and  Day 

N 

29 

it 

0 

.27 

1064 

1064 

3 

Jacquerod  a  n  d  j 

Air,  N, 

{•   23 

u 

0 

.21 

1067.2 

1067 

.4 

Perrot.  .        ,  .  1 

O,  CO 

i 

,_       •     x  (  955  in  air   )      mi    r       •          •  A   r 
Silver.  —  (Freezing)  j  V  .   The  f  reezmg-pomt  of 

silver  is  not  a  constant  temperature  except  under  very 
definite  conditions,  and  this  metal  is  volatile,  thus  making 
it  unsafe  to  use  where  its  vapors  may  attack  platinum 
wires,  as  of  a  thermocouple  whose  electric  properties 
silver  alters  very  considerably. 

Many  determinations  of  this  point  have  been  made,  but 
it  is  only  the  recent  observations  that  take  into  account 
the  effects  of  oxidizing  and  reducing  atmospheres. 

Pure  Ag.  In  Air. 

Pouillet  ......  *  ..............  1000°  C. 

E.  Becquerel  .................  960  and  916 

Violle  .......................  954 

Holborn  and  Wien  .......   970 

Heycock  and  Neville  .....  960  .  5  955 

D.  Berthelot  ............  962  957 

Holborn  and  Day  ........  961  .  5  955 

Melted  silver  exposed  to  the  air  gradually  absorbs 
oxygen,  which  lowers  the  freezing-point,  and  this  latter 


STANDARDIZATION  OF  PYROMETERS.          301 

Ls  not  a  definite  temperature  varying  with  the  rate  of 
cooling,  mass,  and  surroundings.  The  wire  method  gave 
953.6 ±0.9  as  found  by  Holborn  and  Day.  The  freezing- 
point  of  pure  silver  may  be  obtained  in  a  graphite  crucible 
in  an  atmosphere  of  nitrogen,  i.e.,  in  conditions  prevent- 
ing oxidation.  The  uncertainty  of  surely  realizing  a 
definite  temperature  with  silver  renders  it  less  desirable 
than  gold. 

Copper. — (Freezing)  1065°  in  air,  1084°  pure.  Whether  or 
not  the  gold-  or  the  copper-point  was  the  higher  was  long 
an  open  question  in  pyrometry.  The  only  advantage  in 
practice  of  copper  is  its  cheapness,  but  the  fact  that  copper 
has  two  freezing-points  does  not  possess  the  same  disad- 
vantages as  with  silver,  for  the  copper-points  are  very 
definite,  the  higher  one,  1084,  being  that  of  the  pure  metal, 
easiest  obtained  with  a  graphite  crucible,  the  metal  being 
protected  from  the  ah*  by  a  layer  of  powdered  graphite. 
The  lower  value,  1065,  is  given  by  the  wire  method  and 
copper  may  replace  gold  in  this  way.  Values  inter- 
mediate between  1065  and  1084  will  be  obtained  for 
incomplete  protection  from  air,  the  effect  being  due,  as 
explained  by  T.  W.  Richards,  to  the  formation  and  solu- 
tion of  cuprous  oxide,  saturation  of  the  copper  with  the 
oxide  giving  the  point  1065. 

We  may  note  the  f  olio  wing  determinations  of  the  copper- 
points: 

Heycock  and  Neville 1080. 5 

Stansfield 1083 

Holman 1086 

Holborn  and  Day 1084. 1 

The  value  obtained  by  Holborn  and  Day  is  the  only 
one  determined  directly  in  terms  of  the  gas-thermometer. 


302  HIGH  TEMPERATURES. 

Platinum. — (Fusion)  1780°.  As  the  gas-thermometer 
has  not  been  used  above  1150°C.,  all  higher  fixed  points 
must  be  reduced  to  the  gas-scale  by  extrapolation.  Al- 
though the  uncertainty  of  this  point  is  very  considerable, 
perhaps  over  25°,  the  determinations  that  have  been 
made  agree  remarkably.  Thus  Violle,  as  well  as  Holborn 
and  Wien,  and  Holborn  again,  all  get  1780. 

Iridium. — (Fusion)  2250°.  Although  it  is  questionable  if 
temperatures  of  2000°  C.  and  over  can  be  determined  in 
terms  of  the  gas-scale,  it  may,  nevertheless,  be  found 
desirable  to  determine  as  exactly  as  may  be  one  or  more 
fixed  temperatures  in  this  range  by  other  methods,  as 
specific  heat  and  the  laws  of  radiation.  Iridium  and 
osmium  seem  to  be  suitable  for  this  purpose.  Hardly  any 
limit  of  accuracy  can  as  yet  be  placed  upon  such  deter- 
minations. For  indium  the  following  values  have  been 
found : 

Violle 1950°  C. 

Veder  Weyde 2200 

Pietet 2500 

Nernst 2200  to  2240 

Rasch  (computed) 2285 

The  recent  development  of  furnaces  suitable  for  use 
at  these  extreme  temperatures  will  undoubtedly  enable  us 
to  more  sharply  define  this  part  of  the  scale. 

It  is  interesting  to  note  that  at  the  extreme  tempera- 
ture of  the  electric  arc,  3600°  C.,  the  various  radiation 
methods  and  the  specific  heat  method  give  results  agreeing 
to  about  100°  C. 

Other  metals  have  also  been  used  in  the  attempt  to 
determine  fixed  points  and  some  of  the  results  are  given 
in  the  accompanying  table: 


STANDARDIZATION  OF  PYROMETERS. 


303 


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304 


HIGH   TEMPERATURES. 


The  points  which  are  uncertain  or  difficult  of  experi- 
mental determination  are  enclosed  in  brackets. 


— 1084  0 


h.  m.        Time- 


h. 


1050 


00 


10 


COPPER 
FIG.  77. 


The   freezing-point   curves   of   copper,    antimony,    and 
aluminium  are  shown  in  Fig.  77,  where  times  in  minutes 


STANDARDIZATION  OF  PYROMETERS. 


305 


is  plotted  as  abscissa  and  E.M.F.  of  a  90Pt-10Rh  thermo- 
couple as  ordinate.     An  inspection  of  the  copper  curve 


E.M.F.  in  Millivolts 

«r  4* 

A 

R31° 

f-  1*      \ 

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20 

ANTIMONY 
FIG.  78. 

shows  why  this  metal  is  desirable  to  use.     With  aluminium 
rapid  cooling  would  be  fatal  to  an  exact  determination, 


306 


HIGH   TEMPERATURES. 


and  for  this  metal  the  melting  curve  is  also  given,  showing 
the  melting-  and  freezing-points  to  differ.    Antimony  under- 


Freezing 


657°—^ 


•&&• 


•575- 


Time  — 
10430  1040 


10-50 


1110 


ALUMINIUM 
PIG.  79.  • 


goes  great  undercooling,  over  30°  C.,  but  the  maximum 
is  a  very  definite  point. 


STANDARDIZATION  OF  PYROMETERS.          307 

Sometimes  it  is  desired  to  calibrate  a  pyrometer  down 
to  room  temperature,  even  if  in  this  case  the  use  of  a 
mercury-thermometer  is  usually  to  be  preferred.  Use  may 
be  made  of  the  boiling-points  of  water,  aniline  or  naph- 
thaline, and  benzophenone,  or  of  the  tin  freezing-point. 

Water. — 100°  by  definition,  with  a  variation  of  0°.04 
for  a  change  of  1  mm.  in  atmospheric  pressure. 

Aniline. — 184°.l  with  a  change  of  0°.05  per  millimeter. 
This  value  is  probably  correct  to  0.1  degree. 
Naphthaline. — 218°.0,  with  a  change  of  0°.06  per  mm. 
Benzophenone.—  305°.9  with  a  change  of  0°.075  per  mm. 
Metallic  Salts. — The   different  fixed  points  that  have 
been  mentioned  are  not  all  of  a  very  convenient  use.     It 
would  be  preferable  to  have  in  the  place  of  the  metals, 
metallic  salts  for  the  determination  of  the  fixed   points. 
These  salts  fortunately  are  for  the  most  part  without 
action  on  platinum,  which  is  of  great  advantage  for  the 
standardization    of    thermocouples    and    resistance-ther- 
mometers.    There  are  none,  unfortunately,  whose  fusing- 
points  have  been  determined  up  to  the  present  time  in  a 
sufficiently  precise  manner. 

Among  the  most  interesting  to  study  from  this  point  of 
view,  we  may  cite  the  following: 

1  mol.  NaCl  +  1  mol.  KC1 About  650° 

NaCl "  800 

Na2SO< "  900 

Pb205-2Na20 «  100o 

K2S04 «  1070 

MgSO, «  H50 

SiO2-CaO «  1700 

It  is  especially  desirable  to  have  a  more  satisfactory 
point  than  has  as  yet  been  obtained  in  the  interval 
between  the  sulphur-  and  gold-points. 


308  HIGH   TEMPERATURES. 

Table  of  Fixed  Points. — In  the  actual  state  of  our 
knowledge,  the  fixed  points  to  which  we  should  give  pref- 
erence are  summarized  in  the  table  below: 

Boiling.  Freezing. 

Water 100°. 0 

Naphthaline 218  .0 

Sulphur 444  .6 

Tin 232° 

Zinc 419 

Silver 962 

Gold 1065 

Platinum 1780 

Standardization  of  Pyrometers. — The  above  discussion 
has  shown  that  we  possess  a  number  of  fixed  points  which 
have  been  established  with  sufficient  accuracy  to  use 
them  in  the  standardization  of  pyrometers.  For  such 
standardization,  two  courses  are  open  besides  direct 
comparison  with  a  gas-thermometer,  a  proceeding  usually 
out  of  the  question  and  furthermore  rendered  super- 
fluous by  the  establishment  of  these  fixed  points.  When 
its  construction  permits,  a  pyrometer  may  be  calibrated 
by  finding  its  indications  at  two  or  more  of  the  fixed  points, 
or  may  be  compared  with  another  which  has  been  so 
calibrated.  The  latter  method  is  the  one  used  for  ordi- 
nary purposes,  as  in  the  graduation  of  industrial  instru- 
ments, but  for  pyrometers  which  are  to  be  used  as  primary 
standards  the  former  method  should  be  used  when  pos- 
sible. 

We  have  discussed  at  some  length,  in  their  respective 
chapters,  the  methods  of  graduation  for  the  various 
pyrometers  and  it  is  unnecessary  to  further  dwell  on  this 
matter,  except  to  say  that  it  cannot  be  assumed  that  a 


STANDARDIZATION  OF  PYROMETERS.          309 

pyrometer  once  standardized  is  standardized  for  all  time, 
especially  if  it  has  had  hard  usage. 

Standardizing  Laboratories. — Recognizing  the  impor- 
tance of  establishing,  preserving,  and  disseminating  a 
common  and  authoritative  temperature  scale  and  of 
providing  means  of  having  pyrometers  and  other  instru- 
ments certified  as  to  their  accuracy,  some  of  the  govern- 
ments have  established  laboratories,  such  as  the  Physi- 
kalische-Technische  Rerchsanstalt  in  Germany,  the  Na- 
tional Physical  Laboratory  in  England,  and  the  National 
Bureau  of  Standards  *  in  the  United  States,  whose 


*  The  Bureau  of  Standards  tests  and  gives  certificates  for  any 
kind  of  pyrometer,  and  in  this  connection  the  following  quotations, 
from  Bureau  Circular  Xo.  7,  on  "Pyrometer  Testing  and  Heat 
Measurements,"  may  be  of  interest: 

"When  pyrometers  are  submitted  for  test,  it  is  highly  desirable 
that  the  request  for  test  be  accompanied  by  a  statement  giving 
as  far  as  possible  the  conditions  under  which  the  pyrometer  is 
used  (e.g.,  method  of  mounting  pyrometer,  depth  of  immersion, 
kind  of  bath  or  medium  whose  temperature  is  to  be  measured, 
how  the  pyrometer  is  protected,  at  what  temperature  it  is  used, 
and  whether  continuously  exposed  to  these  temperatures,  etc.). 
A  sketch  showing  method  of  use  of  instrument  is  often  very  useful. 
It  is  only  when  accompanied  by  such  information  that  it  is  possible 
to  realize  approximately  the  same  conditions  in  the  test  as  in 
the  actual  use  of  the  pyrometer  and  to  make  a  statement  as  to 
the  order  of  accuracy  that  may  be  attained.  It  also  enables  sug- 
gestions to  be  made  as  to  desirable  modifications  in  the  use  of 
the  instrument  that  may  lead  to  more  satisfactory  results.  .  .  . 

"It  is  desirable,  when  a  thermocouple  is  submitted  for  test,  that 
it  be  accompanied  by  the  galvanometer  with  which  it  is  used. 
The  protecting  sheaths  should  not  be  sent  in. 

"  The  complete  test  of  a  thermocouple  consists  in  a  thorough 
annealing  at  white  heat,  determination  of  the  electromotive  force 
of  the  couple  at  three  or  more  known  temperatures  in  terms  of 
the  standard  scale  of  temperature  of  this  Bureau,  and  the  measure- 
ment of  the  resistance  of  the  couple  (when  cold),  with  accompany- 


310  HIGH  TEMPERATURES. 

functions  are  not  only  testing  instruments  but  carrying 
qn  researches  as  well.  The  German  institution,  the  oldest 
of  these  laboratories,  has  been  one  of  the  most,  potent 
factors  in  the  development  of  excellency  in  German  instru- 
ments, and  has  been  of  immense  service  to  the  industries 
as  well  as  to  the  interests  of  science. 

Electrically  Heated  Furnaces. — For  the  standardization 
of  pyrometers  as  well  as  in  many  other  high-temperature 
problems  it  is  necessary  to  preserve  a  constant  tempera- 
ing  tables  of  corresponding  electromotive  forces  and  temperatures, 
and  when  the  pyrometer-galvanometer  is  submitted  a  table  will 
be  furnished  giving  temperatures  directly  in  terms  of  the  readings 
of  the  galvanometer  joined  to  the  couple.  .  .  . 

"The  test  [of  radiation  and  optical  pyrometers]  consists  in 
determining  the  readings  of  the  instrument  at  three  or  more  known 
temperatures  in  terms  of  the  standard  scale  of  this  Bureau,  together 
with  a  statement  of  directions  and  necessary  precautions  that 
should  be  observed  in  the  use  of  the  pyrometer.  A  table  is  also 
furnished  giving  temperatures  in  terrns  of  readings  of  the  instru- 
ment. .  .  . 

"Testing  of  various  kinds  of  calorimetric  apparatus  and  thermal 
properties  of  fuels,  oils,  and  other  substances  is  undertaken  by 
this  Bureau.  In  cases  of  scientific  or  technical  interest,  special 
investigations  in  heat  measurements  and  allied  subjects  will  be 
carried  out,  such  as  the  determination  of  coefficients  of  expansion 
at  high  temperature,  specific  heats,  boiling-points,  melting-points 
of  metals,  alloys,  minerals,  etc.  .  .  . 

"It  is  the  desire  of  the  Bureau  to  cooperate  with  manufacturers, 
scientists,  and  others  in  bringing  about  more  satisfactory  conditions 
relative  to  weights,  measures,  measuring  instruments,  and  thermal 
constants,  and  to  place  at  the  disposal  of  those  interested  such 
information  relative  to  these  subjects  as  may  be  in  its  possession. 

"It  is  also  desired  to  aid  in  the  solution  of  specific  scientific 
problems  arising  in  technical  or  scientific  work,  coming  within 
the  scope  of  the  Bureau,  and  to  this  end  correspondence  is  invited. 

"Persons  interested  in  pyrometric  problems  are  welcome  to 
visit  the  laboratories  of  the  Bureau,  where  many  of  the  leading 
types  of  pyrometers  may  be  seen  in  operation." 


STANDARDIZATION  OF  PYROMETERS.          311 

ture  for  a  considerable  time  and  to  be  able  to  reproduce  a 
given  temperature  very  exactly. 

Electrically  heated  resistance-furnaces  best  serve  these 
ends,  and  great  improvements  have  been  made  in  their 
construction  in  recent  years. 

Furnaces  wound  with  nickel  wire  of  1  to  2  mm.  diameter 
on  porcelain  have  been  used  considerably,  but  they  are 
slow  in  heating  up  and  their  upper  limit  is  about  1200°  C. 
if  the  furnace  is  to  be  used  frequently,  although  for  a 
single  heating  1450°  C.  may  be  attained  with  care.  Plati- 
num wire  has  been  used  to  attain  higher  temperatures,  but 
the  use  of  this  material  in  wire  form  is  very  expensive  for 
heating. 

Heraeus  has  made  electric  heating  to  1500°  C.  generally 
accessible  by  the  substitution  of  platinum-foil  for  the  wire, 
weighing  about  1.5  grammes  per  square  centimeter  or 
having  a  thickness  of  about  0.007  mm.  This  reduces  the 
cost  of  a  platinum  furnace  very  greatly,  and  has  the  further 
advantages  of  giving  greater  uniformity  of  heating  and 
attaining  safely  higher  temperatures  than  with  wire-wound 
furnaces,  and  instead  of  taking  an  hour  or  more,  five  or 
ten  minutes  suffice  to  heat  a  foil  furnace  to  1400°  C. 
Figs.  38  and  61  illustrate  such  furnaces.  Above  1500°  C. 
chemical  action  sets  in  between  the  platinum  and  material  of 
the  tubes  tried  thus  far,  so  that  although,  as  far  as  the 
platinum  is  concerned,  1700°  C.  could  be  maintained,  yet 
the  present  upper  limit  for  long  periods  of  heating  is  1500°. 

For  very  high  temperatures,  up  to  2100°,  the  iridium- 
tube  furnaces  of  Heraeus  may  be  used  (p.  169),  as  they  have 
been  with  success  by  Nernst  and  others  in  the  study  of 
vapor  pressures  at  these  temperatures. 


CHAPTER  XIV. 
CONCLUSION. 

IN  closing  this  account  it  will  not  be  useless  to  call  the 
attention  of  investigators  to  points  whose  study  seems  the 
most  needed  to  aid  the  progress  of  our  knowledge  of  high 
temperatures.  We  will  mention  first  the  precise  deter- 
mination of  the  fixed  points  serving  for  the  graduation  of 
pyrometers;  there  does  not  exist  at  the  present  time 
above  the  boiling-point  of  sulphur  any  temperature  known 
certainly  to  1°.  For  the  ebullition  of  zinc,  the  fusing  of 
silver  and  that  of  gold,  which  are  at  present  the  best  known, 
the  uncertainty  may  be  10°  for  the  first,  but  is  probably 
less  than  5°  for  the  fusing-points.  It  would  be  well  also  to 
try  and  find  substances  serving  for  fixed  points  that  are  more 
convenient  to  handle  than  the  metals — salts,  for  example — 
which  do  not  attack  platinum  either  when  they  are  melted 
or  when  they  are  vaporized;  these  substances  should  be 
found  easily  and  economically  in  a  state  of  purity;  they 
should  possess  well-defined  points  of  fusion  and  of  ebullition, 
which  is  not  always  the  case  when  the  crystallized  salt 
has  several  dimorphous  varieties. 

A  second  very  important  point  for  investigations  of 
great  precision  would  be  the  determination  of  the  general 
form  of  the  function  which  connects  electrical  resistance 
with  temperature.  One  cannot  hope  to  determine  com- 
pletely this  function  with  the  value  of  its  parameters, 
because  there  are  not  two  samples  of  platinum  having 

312 


CONCLUSION.  313 

exactly  the  same  resistance;  it  is  necessary  in  each  case 
to  make  the  calibration  by  means  of  fixed  fusing-  or 
boiling-points.  The  work  of  Hey  cock  and  Neville  is  a 
long  step  towards  the  accomplishment  of  this  end.  The 
number  of  such  points  to  compare  depends  on  the  number 
of  parameters  contained  in  the  formula.  By  his  researches 
in  this  matter,  Prof.  Silas  Holman  greatly  facilitated 
the  use  of  thermoelectric  couples  by  showing  that  it  is 
sufficient  between  0°  and  1800°  to  use  a  logarithmic 
formula  containing  only  two  parameters. 

For  the  measurement  of  exceedingly  high  temperatures, 
which  can  be  effected  only  by  methods  employing  radiation 
and  depending  upon  extrapolations  often  considerable,  it 
would  be  very  useful  to  determine,  with  greater  precision 
than  has  been  done  as  yet,  the  law  of  the  radiation  from 
a  rigorously  black  body  (enclosed  space),  either  for  a 
monochromatic  radiation,  as  radiation  transmitted  by  the 
red  glasses,  or  for  the  totality  of  heat  radiations.  But 
such  a  study  can  be  of  value  only  on  the  condition  of  pos- 
sessing a  very  great  precision,  difficult  to  attain  actually 
on  account  of  the  uncertainty  which  still  exists  as  to  the 
temperatures  directly  measurable.  Great  advances  have 
been  made  in  this  field  of  pyrometry  in  recent  years  by 
Paschen,  Lummer  and  his  associates  at  the  Reichsanstalt  on 
the  experimental  side,  and  by  Wien,  Boltzmann  and  Planck 
on  the  theoretical  side. 

The  Stefan-Boltzmann  law  has  been  shown  to  apply 
from  -200°  C.  up  to  1600°  C.,  with  an  accuracy  of  better 
than  one  per  cent  for  total  radiation.  Wien's  spectral 
energy  law  and  his  displacement  law  for  monochromatic 
radiation  are  in  exact  agreement  with  the  preceding 
certainly  up  to  2000°  C.,  and  probably  at  the  temperature 
of  the  arc,  3600°  C.,  and  no  certain  discordance  has  been 
found  in  the  results  using  these  various  methods  in  the 


314  HIGH   TEMPERATURES. 

estimation  of  the  effective  temperature  of  the  sun,  about 
6000°  C.  Le  Chatelier's  formula  for  monochromatic  light 
seems  also  to  be  in  agreement  with  the  others.  The  exper- 
imental comparison  and  verification  of  these  formulae  have 
been  greatly  facilitated  by  the  development  of  electric- 
resistance  furnaces,  and  a  convenient  form  of  experimental 
black  body. 

The  establishment  of  a  satisfactory  temperature  scale 
to  2000°  C.  and  beyond  is  perhaps  the  most  pressing  problem 
in  pyrometry  to-day,  as  witness  the  temperatures  realized 
in  the  Moissan  furnace,  the  thermite  process,  and  many 
pyrochemical  and  metallurgical  operations.  The  laws  of 
radiation,  we  have  seen,  will  serve  as  a  tentative  scale,  which 
is,  however,  without  significance  as  an  extension  of  the 
gas-scale  proper,  as  the  degrees  of  temperature  measured 
optically  in  this  high  range  may  or  may  not  have  any 
relation  to  those  given  by  a  gas-thermometer.  It  may  be 
possible,  however,  to  intercompare  other  methods  with 
the  radiation.  Thus  Berthelot's  system  of  gas-ther- 
mometry  can  undoubtedly  be  carried  higher  successfully. 
Again,  purely  thermodynamic  and  also  chemical  methods  of 
measuring  extreme  temperatures  have  been  suggested, 
among  others  by  Nernst,  who  would  make  use  of  the  ex- 
pression involving  the  dissociation  of  a  gas  as  follows : 

dlogK 
dT     ' 

where  Q  is  the  heat  of  formation  of  carbonic  acid  at  the 
temperature  T,  R  the  gas  constant,  and  K  the  coefficient  of 
mass  action,  which  is  dependent  upon  the  pressure  and 
degree  of  dissociation  of  the  gas  mixture. 

Finally,  if  the  intensity  of  radiation  per  unit  area  could 
be  exactly  determined  in  C.G.S.  units,  as  was  tried  by 


CONCLUSION.  315 

Lummer  and  Kurlbaum,  still  another  absolute  scale  would 
be  had.  At  very  high  temperatures,  this  method  is  more 
promising  than  at  lower,  because  the  light-intensity  in- 
creases relatively  less  rapidly. 

At  the  Paris  congress  of  1900,  Barus  thus  summarized 
recent  progress:  The  actual  state  of  pyrometry  is  most 
encouraging.  It  is  clear  that  in  a  few  years  from  now 
pyrometry  will  be  in  possession  of  a  series  of  constants  as 
exact  as  those  of  the  best-developed  branches  of  physics. 
In  Germany,  a  gas-thermometer  impermeable  to  the 
thermometric  gas  and  rigid  up  to  white  heat  has  been 
found,  thanks  to  the  efforts  of  Holborn,  Wien,  and  Day, 
at  the  Reichsanstalt.  In  England,  the  efforts  of  Cal- 
lendar,  Griffiths,  and  others  to  construct  an  instrument 
of  remarkable  sensibility  from  the  absolute  zero  to  1000°  C. 
have  been  crowned  with  merited  success. 

In  France,  the  best  practical  pyrometer  has  been  found 
by  Le  Chatelier,  and  D.  Berthelot  has  devised  an  optical 
method  for  the  measurement  of  temperatures  in  absolute 
value,  independent  of  the  form  and  size  of  the  thermomet- 
ric envelopes,  and  whose  upper  limit  is  indefinite ;  for  since 
we  have  learned,  thanks  to  the  great  discovery  of  Nemst, 
that  the  refractory  earths  become  conductors  at  high  tem- 
peratures, it  has  become  possible  to  heat  electrically  the 
most  infusible  substances  up  to  the  highest  degrees  on  the 
scale. 

With  a  thermostat  of  this  kind,  Berthelot 's  pyrometric 
method  in  absolute  value  marches  side  by  side  with  the 
most  advanced  practical  progress  realized  by  Moissan;  in 
other  terms,  pyrometry  in  absolute  value  is  only  limited 
to-day  by  the  difficulty  of  the  manufacture  of  apparatus 
in  refractory  materials. 

In  closing  we  beg  to  call  attention  to  a  fact  of  some 
importance.  The  measurement  of  high  temperatures 


316  HIGH  TEMPERATURES. 

possesses  certainly  great  interest  from  the  point  of  view 
of  the  progress  of  pure  science;  but  it  is  to  be  noted  that 
industrial  needs  have  stimulated  the  partial  solution  of 
this  problem:  Wedgwood,  the  china  manufacturer,  seek- 
ing to  better  his  processes;  similarly,  Seger,  at  the  Berlin 
works,  occupied  himself  exclusively  with  ceramic  prod- 
ucts; Siemens  sought  to  regulate  the  making  of  steel; 
the  engineers  of  the  Paris  Gas  Company  wanted  a  means 
of  control  over  the  distillation  of  oil;  Le  Chatelier  studied 
the  thermoelectric  pyrometer  in  the  course  of  investiga- 
tions on  the  baking  of  clay  and  on  the  manufacture  of 
cements;  he  studied  the  optical  pyrometer  at  the  request 
of  a  Sheffield  steel  manufacturer,  Hadfield,  who  desired 
for  his  works  a  pyrometer  uniting  accuracy  with  simplicity 
of  use.  Roberts-Austen,  director  of  the  mint  at  London, 
devoted  all  his  efforts  for  many  years  to  the  study  of 
industrial  alloys,  obtaining  results  of  great  value,  largely 
due  to  the  utility  of  the  recording-pyrometer. 

This  incentive  of  practical  needs  on  the  progress  of 
science  is  not  surprising.  The  savants  who  founded 
chemistry  recognized  no  distinction  between  pure  and 
applied  science.  Lavoisier,  Chevreul,  Gay-Lussac,  Dumas, 
Thenaud,  H.  Sainte-Claire-Deville  went  indifferently  into 
the  laboratory  or  the  works.  It  is  the  present  trend  of 
our  teaching  methods  that  has  opened  a  breach  increasing 
in  size  every  day  between  theory  and  practice. 

In  the  scientific  laboratories  all  efforts  follow  in  well- 
beaten  paths.  There  one  is  free  to  choose  his  subjects  of 
study  according  to  his  caprices;  one  may  be  easily  guided 
by  artificial  preoccupations,  concerning  themselves  but 
very  indirectly  with  a  study  of  nature.  Finally,  one  may 
have  confidence  for  a  long  time  in  erroneous  results  with- 
out having  any  inkling  of  the  error  committed.  In  in- 
dustrial works  it  is  quite  otherwise:  one  cannot  remain 


CONCLUSION.  317 

stationary  upon  problems  already  solved;  in  spite  of  one's 
self  one  must  march  ahead.  Subjects  of  study  obtrude 
and  must  necessarily  be  taken  up  in  the  order  of  their 
real  importance.  Wrong  conclusions  are  made  evident 
by  their  contradictions  at  each  instant  with  facts  that 
one  cannot  refuse  to  see.  These  conditions  explain  how 
laboratories  attached  to  industrial  works,  with  their  in- 
sufficient personnel  absorbed  largely  in  other  matters, 
with  their  rudimentary  material,  come  nevertheless  to 
contribute  largely  to  the  process  of  pure  science.  All  the 
progress  so  important  in  the  chemistry  of  iron  is  made 
to-day  in  industrial  works  and  in  the  laboratories  attached 
to  them. 

It  is  not  in  chemistry  alone  that  practical  needs  have 
manifested  this  creative  power.  It  was  in  studying  the 
boring  of  cannon  that  Rumford  met  the  notion  of  the 
conservation  of  energy ;  it  was  in  reflecting  upon  the  steam- 
engine  that  Sadi-Carnot  established  the  basis  of  thermo- 
dynamics; it  was  in  seeking  to  perfect  light-house  lenses 
that  led  Fresnel  to  his  investigations  on  the  theory  of 
light. 


BIBLIOGRAPHY. 

(The  heavy  figures  refer  to  volumes.) 

GENERAL  WORKS. 

Weinhold. — Principles  of  construction  of  pyrometers.   Pogg.  Ann., 

149  (1873),  p.  186. 
C.  H.  Bolz. — Die  Pyrometer,  Eine  Kritik  der  bisher  construirten 

hoher  Temperaturmesser  in  wissenschaftlich-technische   Hin- 

sicht  (1888). 
C.  Bams. — Die  physikalische  Behandlung  und  die  Messung  hoher 

Temperaturen  (1892,  Leipzig). — Bull.  U.  S.  Geological  Survey 

No.  54  (1889). 
Kayser. — Handbuch  der  Spectroscopie,  Bd.  2,  1902.    Summary  of 

radiation  methods. 
CaUendar. — Measurement  of  Extreme  Temperatures.  Nature  (1899) , 

59. 
C  W.  Waidner. — Methods  of  Pyrometry.     Proc.  Eng.  Soc.  Western 

Pennsylvania,  Sept.  1904. 

NORMAL  SCALE  OF  TEMPERATURES. 

Carnot. — Reflections  on  the  motive  power  of  fire. 

Lippmann. — Thermodynamics,  p.  51. 

Thomson   and   Joule. — Philosophical    Transactions    of    the    Royal 

Society,  42  (1862),  p.  579. 

Thomson  (Lord  Kelvin). — Collected  Papers,  1,  p.  174. 
Lehrfeldt— Philosophical  Magazine,  45  (1898),  p.  363. 
CaUendar.— Phil.  Trans.,  178  (1888),  pp.  161-220. 
RegnauU. — Account  of  his  investigations,  1  (1847),  p.  168. 
Chappuis. — Studies   of   the   gas-thermometer.     Trav.    du   Bureau 

International  des  Poids  et  Mesures,  6  (1888). 
Chappuis  and  Harker. — Trav.  et  Mem.  du  Bureau  Int.  des  Poids 

et  Mesures,  1900.     Phil.  Trans.,  1900. 

Schreber. — Absolute  Temperature.     W.  Beibl.,  22  (1898),  p.  297. 

319 


320 

D.  Berthelot. — Reduction  of  gas-thermometer  readings  to  the  ab- 

solute scale.     Trav.  et  Me"m.  du  Bureau  Int.,  13,  1903;   C.  R., 
138  (1904),  p.  1153. 

Boltzmann. — On  the  determination  of  absolute  temperature.    Wied. 
Ann.,  53  (1894),  p.  948. 

E.  Mach. — Theory  of  Heat. 

Callendar. — Thermodynamical  correction  to  gas-thermometer.  Phil. 

Mag.,  May  1903. 

Rose-Innes.— Phil.  Mag.  (6),  2  (1901),  p.  130. 
Pellat.—C.  R.,  136,  p.  809  (1903). 


GAS-PYROMETERS. 

Prinsep.— Ann.  Chim.  et  Phys.,  2d  Series,  41  (1829),  p.  247. 
PouilleL— Treatise  on  Physics,  9th  ed.  (1858),  1,  p.  233;    Comptes 

Rendus,3(1836),p.782. 

Ed.  Becquerel—C.  R.,  57  (1863),  pp.  855,  902,  955. 
Sainte-Claire-Deville  and  Troost.—C.  R.,  90  (1880),  pp.  727,  773; 

45  (1857),  p.  821;  49  (1859),  p.  239;  56,  p.  977;  57  (1863),  pp. 

894,  935;   98  (1884),  p.  1427;   69  (1864),  p.  162;  Ann.  Chim. 

et  Phys.  (3),   58  (1860),  p.  257;  Repert.  Chim.  Appl.  (1863), 

p.  326. 
Violle.— Specific  heat  of  platinum.     C.  R.,  85   (1877),  p.  543  — 

Specific  heat  of  palladium.     C.  R.,  87  (1878),  p.  98;  89  (1879), 

p.  702. — Boiling-point  of  zinc.     C.  R.,  94  (1882),  p.  721. 
V.  and  C.  Meyer.— Density  of  halogens.  Ber.  D.  Ch.  Ges.,  12  (1879), 

p.  1426. 
Barus.— Bull.  U.  S.  Geological  Survey  No.  54  (1889);    Phil.  Mag. 

(5),  34  (1892),  p.  1. — Report  on  Pyrometry,  Congress  at  Paris, 

1900'. 
Regnault. — Account  of  his  experiments,   1,  p.  168   (Paris,  1847); 

Me*m.  de  1'Institut,  21  (1847),  pp.  91,  110;  Ann.  Chim.  et  Phys. 

(3),  68  (1861),  p.  89. 
Holborn  and  Wien. — Bull,  de  la  Soc.  pour  1'encouragement  (5),  1 

(1896),  p.  1012;  Wied.  Ann.,  47  (1892),  p.  107;   56  (1895),  p. 

360;  Zeits.  f vjr  Instrum.  (1892),  p.  257. 
Crafts  and  Meier.— Vapor  density  of  iodine.     C.  R.,  90  (1880),  p. 

690. 

Langer  and  V.  Meyer. — Pyrochemical  Researches  (Brunswick),  1885. 
Jolly.— Pogg.  Ann.,  Jubelband  (1874),  p.  97. 


BIBLIOGRAPHY.  321 

Randall— Permeability  of  platinum.     Bull.  Soc.  Chim.,  21  (1898), 

p.  682. 

Mallard  and  Le  Chatelier. — Ann.  des  Mines,  4  (1884),  p.  276. 
J.  R.  Erskine  Murray. — On  a  new  form  of  constant-volume  air- 
thermometer.       Edinburgh  Proc.,  21  (1896-97),  p.  299,  and 

Journ.  Phys.  Chem.,  1  (1£97),  p.  714- 

J.  Rose-Innes. — The    thermodynamic    correction  for  an  air-ther- 
mometer, etc.     Nature,  58  (1898),  p.  77;  Phil.   Mag.  (5),  45 

(1898),  p.  227;    50  (1900),  p.  251;   Proc.  Phys.  Soc.  London,  16 

(1),  (1898),  p.  26. 
Chappuis.— Phil.  Mag.  (5),  50  (1900),  p.  433;  (6),  3  (1902),  p.  243; 

Report  for  Paris  Congress,  1900;    Jour,  de  Phys.,  Jan.  1901, 

p.  20. 
D.  Berthelot. — On  a  new  method  of  temperature  measurement.     C. 

R.,  120  (1895),  p.  831;    Ann.  Chim.   et  Phys.  (7),  26  (1902), 

p.  58. 
Hottorn  and  Day. — Wied.  Ann.,  68  (1899),  p.  817,  and  Am.  Jour. 

(4),  8  (1899),  p.   165;    Zeitscher.  Instrum.,  May  1900;   Am. 

Jour.  (4),  10  (1900),  p.  171,  and  Drude's  Ann.,  2  (1900),  p.  505. 
Chappuis  and  Harker. — Trav.  et  Mem.  du  Bureau  Int.  des  Poids, 

etc.,  1900,  1902.— Phil.  Trans.,  1900. 
Calendar.— Phil.    Mag.,   48   (1899),  p.  519;    Proc.  Roy.  Soc.,  50 

(1891),  p.  247. 

Cattendar  and  Griffiths. — Phil.  Trans.,  182  (1891). 
D.  Berthelot.  —  On  gas-thermometers  and  the  reduction  of  their 

indications  to  the  absolute  scale.  Trav.  et  Mem.  du  Bureau  Int., 

13,  1903. 

Travers. — Studies  hi  Gases  (Macmillan). — Proc.  Roy.  Soc.,  70,  p.  485. 
Kapp.— Ann.  der  Phys.,  5  (1901),  p.  905. 
Wiebe  and  Bottcher. — Gas-thermometry,  Berich.   Berlin  Akad.,  44, 

p.  1025,  Inst'kunde,  1888. 
Jacquerod  and  Perrot. — Various  gases  hi  quartz.   C.  R.,  138  (1904), 

p.  1032. 

CALORIMETRIC  PYROMETER. 

Violle.— Boiling  and  fusing  points.     C.  R.,  89  (1879),  p.  702. 
Le  Chatelier. — Sixteenth  Congress  of  the  Societe  technique  de  Pin- 
dust  rie  du  gaz  (June  1889). 
Euchene. — Thermal  relations  in  the  distillation  of  oil.     (Monograph.) 


322  B1BLIOGRAIHY. 

Ferrini—  Rend.  Lomb.  35  (1902),  p.  703. 

Berthelot. — Calorimetry.     Aim.  Chim.  et  Phys.,  4th  Series,  20.  \\ 

109;  5th  Series,  5,  p.  5;  5th  Series,  10,  pp.  433,  447;  5th  Series, 

12,  p.  550. 


ELECTRICAL-RESISTANCE  PYROMETER. 

W .  Siemens.— Proc.  Royal  Soc.,  19  (1871),  p.  351 ;  Bakerian  Lec- 
ture, 1871 ;  Transactions  of  the  Society  of  Telegraph  Engineers, 
1879;  British  Association,  1874,  p.  242. 

A/u&r.— Pogg.  Ann.,  103  (1S5S),  p.  176. 

Benoit.— C.  R.,  76  (1873),  p.  342. 

Calendar.— Phil.  Trans,  of  R.  S.f  178  (1888),  pp.  160-230;  Proc. 
Roy.  Soc.  London,  41  (1886),  p.  231,  and  Phil.  Trans.,  1887; 
Phil.  Trans.  (1S92),  p.  119  (with  Griffiths'). — Platinum  pyrome- 
ters. Iron  and  Steel  Institute,  May  1892;  Phil.  Mag.,  32 
(1891),  p.  104;  33  (1S92\  p.  220.— Proposals  for  a  standard 
scale  of  temperatures.  B.  A.  Report,  1899;  Phil.  Mag.,  47 
(1899),  pp.  191,  519,  is  a  resurnS  of  the  question;  Phil.  Trans., 
199  (1902),  p.  1. 

Heycock  and  NeviUt. — Determination  of  high  temperatures.  J.  of 
Chem.  Society,  68  (1895),  pp.  160,  1024;  Phil.  Trans.,  202  A, 
pp.  1-69. 

Barns.— Amer.  Jour.  (3),  36  (1SS3),  p.  427. 

Holborn  and  Wien.— Ann.  der  Phys.  u.  Chem.,  47  (1892),  p.  107;  56 
(1895),  p.  360;  Bull,  de  la  Soc.  d'encouragement ,  5th  Series, 
1(1896),  p.  1012. 

Chappuis  and  Harker. — A  comparison  of  platinum  and  gas  ther- 
mometers made  at  the  B.  Int.  des  Poids  et  Mesures.  B.  A. 
Report,  1899;  Trav.  et  Mem.  du  Bureau  Int.  des  Poids  et 
Mesures,  1900,  1902;  Phil.  Trans.,  1900;  Jour,  de  Phys.,  Jan. 
1901. 

Applsyard.— Phil.  Mag.  (5\  41  (1S96),  p.  62. 

I>idbon.— Phil.  Mag.  (5\  44  (1897),  p.  445;  45  (1898),  p.  525. 

Wade.— Wied.  Beibl.,  23  (1S99),  p.  963;  Proc.  Cainbr.  Soc.,  9  (1898), 
p.  526. 

Waidner  and  MaUory.— Phys.  Rev.,  S,  p.  193  (1S99). 

Barnes  and  Mclntosh. — New  form  of  platinum  thermometer.  Phil. 
Mag.,  6  (1903),  p.  353. 


BIBLIOGRAPHY.  323 

Whipple. — Temperature  indicator,  etc.  Phys.  Soc.(LoncL),  18  (1902), 
p.  235. 

Chree. — Platinum  Thermometry  at  the  Kew  Observatory.  Proc. 
Roy.  Soc.,67,  p.  3. 

Harker. — On  the  high-ten  p  ;rature  standards  of  the  National  Phys- 
ical Laboratory.  Proc.  Roy.  Soc.,  73  (1904),  p.  217. 


THERMOELECTRIC   PYROMETER. 

Becquerel. — Ann.  Chim.  et  Phys.,  2d  Series,  31  (1826),  p.  371. 

PouilleL— Traite  de  Physique,  4th  Ed.,  2,  p.  684;  C.  R.,  3,  p.  786. 

Ed.  Becquerel. — Annales  du  Conservatoire,  4  (1864),  p.  597;  C.  R., 
55  (1862),  p.  826;  Ann.  de  Chim.  et  de  Phys.,  3d  Series,  68 
(1863),  p.  49. 

Tail.— Trans.  Roy.  Soc.  Edinb.,  27  (1872-73),  p.  125. 

RegnauU. — Account  of  investigations  on  heat-engines,  1,  p.  240. — 
C.R.,21(1847),p.240. 

Knott  and  MacGregor.— Trans.  Roy.  Soc.  Edinb.,  28  (1876-77), 
p.  321. 

Le  Chatelier.— Thermoelectric  pyrometer.  C.  R.,  102  (1886),  p. 
819;  Journal  de  Phys.,  2d  Series,  6,  Jan.  1887;  Genie  civil, 
March  5,  1887;  16th  Congress  of  the  Socie'te'  technique  de 
Tindustrie  du  gaz,  June  1889;  Bull,  de  la  Socie'te  de  Pencou- 
ragement  (1892);  Bull.  Soc.  Chim.  Paris,  47  (1887),  p.  42. 

Barus. — Washington,  1889,  Bull,  of  the  U.  S.  Geological  Survey 
No.  54,  No.  103  (No.  54  contains  a  very  complete  historical 
account  of  the  whole  subject  of  pyrometry) ;  Phil.  Mag.  (5), 
34  (1892),  p.  376;  Am.  Jour.,  36  (1888),  p.  427;  47  (3),  (1894), 
p.  366;  48,  p.  336. 

Holborn  and  Wien.— Wied.  Ann.,  47  (1892),  p.  107;  56  (1895),  p. 
360;  Zeit.  des  Vereines  deutscher  Ingenieure,  41  (1896),  p. 
226;  Stahl  und  Eisen,  16,  p.  840. 

Roberts- Austen. — Recent  progress  in  pyrometry.  Trans.  Am.  In- 
stitute of  Mining  Engineers,  1893.  (See  also  Recording  Py- 
rometers.) 

Quincke— Ceramic  insulators  for  very  high  temperatures.  Zeit. 
des  Veremes  deut.  Ingenieure,  40,  p.  101. 

Struthers. — Thermoelectric  pyrometer  of  Le  Chatelier.  School  of 
Mines  Quarterly,  New  York,  12. 


324  BIBLIOGRAPHY. 

E.  Damour. — Bull,  de  1'Assoc.  amicale  des  anciens  eleves  de  1'Ecole 

des  Mines  (March  1889). 
H.  Howe. — Pyrometric  data.     Engineering  and  Mining  Journal,  50 

(1890),  p.  426. 
Holborn  and  Day. — On  the  melting-point  of  gold.     Drude's  Ann., 

4  (1)  (1901),  p.  99;  Am.  Jour,  of  Sci.,  11,  Feb.  1901,  p.  145.— 

On  the  thermoelectric  properties  of  certain  metals.     Sitz.  Berl. 

Akad.  (1899),  p.  69;    Am.  Jour,  of  Sci.  (4),  8  (1899),  p.  303; 

Mitth.  Phys.-tech.  Reichsanst.,  37  (1899). 
Stansfield.— Phil.  Mag.  (5),  46  (1898),  p.  59. 

Holman.— Phil.  Mag.,  41  (1896),  p.  465;  Proc.  Am.  Acad.,  31,  p.  234. 
Holman,  Lawrence  and  Barr. — Phil.  Mag.,  42  (1896),  p.  37;    Proc. 

Am.  Acad.,  31,  p.  218. 

Schoentjes. — Arch,  de  Phys.  (4),  5  (1898),  p.  136. 
Noll. — Thermoelectricity  of  chemically  pure  metals.     Wied.  Ann., 

1894,  p.  874. 
Steinmann. — Thermoelectricity  of  certain  alloys.     C.  R.,  130  (1900), 

p.  1300;  131  (1900),  p.  34. 

Belloc.— Thermoelectricity  of  steels.     C.  R.,  131  (1900) ,  p.  336. 
Lehrfeldt. — Compensation    apparatus   for   thermoelectric    measure- 
ments.    Phil.  Mag.,  5  (1903),  p.  668. 
Raps.—Zs.  Instrument^.,  15  (lr,95),  p.  215. 
Lindeck  and  Roihe  —  Instrument'!-:.,  20  (1900),  p.  292. 
Carpenter.— Instrument'k.,  21  (1901),  p.  188. 
Franke.— Elektrotech.  Zs.,  24  (1903),  p.  978. 
D.  Berthelot.—On  the  graduation  of  couples.     C.  R.,  134  (1902),  p. 

983. 
Harder.— Direct-reading  potentiometer.     Phil.  Mag.  (6),  6  (1903), 

p.  41. 

Thiede. — Freezing-point  apparatus.  Zs.  Angew.  Ch.,  15,  1902,  p.  780. 
Lindeck  and  Rothe. — The   standardization  of   thermo-elements  for 

high-temperature  measurements  (as  carried  out  at  the  Phys. 

Tech.  Reichsanstalt).     Zs.  Instrument'k.,  20  (1900),  p.  285. 
Howe. — Metallurgical  laboratory  notes  (expts.  with  thermo-couples) 

1902. 
Nichols. — Temperature  of  flames,  etc.,  with  thermo-couple.     Phys. 

Rev.,  10  (1900),  p.  234. 


BIBLIOGRAPHY.  325 


LAWS  OF  RADIATION. 

EARLY   WORK. 

Newton. — Opuscula  Mathematica,  2,  p.  417. 

Dulong  and  Petit.— Ann.  Chim.  et  Phys.,  7  (1817),  pp.  225  and  337. 

Kirchoff.—Pogg.  Ann.,  109  (1860),  p.  275;    Ann.  Chim.  et  Phys.,  59 

(1860),  p.  124. 
B.  Stewart.— Edinburgh  Trans.,  1858;  Proc.  Roy.  Soc.,  10  (1860),  p. 

385. 

Provostaye  and  Desains.—Ann.  Chim.  et  Phys.,  1860-1865. 
Draper.— Am.  Jl.f  4  (1847),  p.  388. 
BecquereL— C.  R.,  55  (1862),  p.  826. 
Clausius.— Pogg.  Ann.,  121  (1864),  p.  1. 
F.  Rosetti.—Phil.  Mag.  (5),  7,  1879,  pp.  324,  438,  537. 
Violle.— C.  R.,  88  (1879),  p.  171;    92  (1881),  pp.866,  1204;  105 

(1887),  p.  163. 

Weber.— Wied.  Ann.,  32  (1887),  p.  256. 
Tait.— Edinb.  Proc.,  12  (1884),  p.  531. 
Tyndall. — Phil.  Mag.,  28  (1864) ,  p.  329. — The  laws  of  radiation  and 

absorption.     Mem.  by  Prevost,  Stewart,  Kirchoff  and  Bunsen, 

edited  by  D.  B.  Brace.     Am.  Bk.  Co.,  1902. 

RECENT  WORK. 

Kayser. — Handbuch  des  spectroscopie,  2,  1902.  (Contains  an 
admirable  summary  of  the  work  on  radiation.) 

Drude. — Theory  of  Optics  (Engl.  Trans,  pub.  by  Longmans). 

Stefan. — On  the  relation  between  heat  radiation  and  temperature. 
•Wien.  Ber.,  79,  B.  2  (1879),  p.  391. 

Schleirmacher.—On  Stefan's  law.     Wied.  Ann. ,  26  (1885) ,  p.  287. 

Boltzmann. — Reduction  of  Stefan's  law.  Wied.  Ann.,  22  (1884),  p. 
291. 

Paschen. — On  the  emission  of  heated  gases.  Wied.  Ann.,  50  (1893), 
p.  409;  51  (1894),  p.  1;  52  (1894),  p.  209. — On  the  emission  of 
solids.  Wied.  Ann.,  49  (1893),  p.  50;  58  (1896),  p.  455;  60  (1897), 
p.  662;  Astrophys.  Jl.,  2  (1895),  p.  202.— On  black  body  radi- 
ation. Wied.  Ann.,  60  (1897),  p.  719;  Berl.  Ber.  (1899),  p.  959; 
Ann.  der  Phys.,  4  (1901),  p.  277;  6  (1901),  p.  646. 

Paschen  and  Wanner. — On  a  photometric  method,  etc.  Berl.  Ber. 
(1899),  p.  5. 


326  BIBLIOGRAPHY. 

Wanner. — Photometric  measurement  of  black  body  radiation.  Ann. 
derPhys.,2(1900),p.  141. 

Ftry—  Radiation  from  oxides.  Ann.  Chim.  Phys.  (7),  27  (1903),  p. 
433. 

Petravel. — Heat  dissipated  by  platinum,  etc.  Phil.  Trans.,  191 
(1898),  p.  501;  197  (1901),  p.  229. 

Milliken. — Polarization  of  light  from  incandescent  surfaces.  Phys, 
Rev.,  3  (1895),  p.  177. 

Langley. — Distribution  of  energy  in  solar  spectrum,  etc.  Am. 
Jl.,  31  (1886),  p.  1;  36  (1888),  p.  367;  Phil.  Mag.  (5)  26  (1888), 
p.  505. 

Wilson  and  Gray. — Temperature  of  arc  and  sun.  Proc.  Roy.  Soc, 
55  (1894),  p.  250;  58  (1895),  p.  24. 

W.  Michelson. — Theoretical  study  of  the  distribution  of  energy  in 
the  spectra  of  solids.  Jl.  de  Phys.  (2),  6  (1887),  p.  467;  Phil. 
Mag.  (5),  25  (1888),  p.  425;  Jl.  Russian  Phys.-Chem.  Soc..  34 
(1902),  p.  155.  ^ 

Violle. — The  radiation  of  incandescent  bodies.  Jl.  de  Phys.  (3), 
1  (1892),  p.  298;  C.  R.,  114,  p.  734;  115,  p.  1273  (1892).— 
Radiation  from  refractory  bodies  heated  in  the  electric  furnace. 
C.  R.,  117  (1893),  p.  33. 

St.  John. — On  the  equality  of  light  emissivities  at  high  tempera- 
tures, etc.  Wied.  Ann.,  56  (1895),  p.  433. 

Kurlbaum. — On  the  new  platinum  light  unit  of  the  Phys.  Tech. 
Reichsanstalt.  Verh.  Phys.  Ges.  (Berlin),  14  (1895),  p.  56. 

Larmor. — On  the  relations  of  radiation  to  temperature.  Nature, 
62  (1900),  p.  562;  63,  p.  216. 

Guillaume. — The  laws  of  radiation  and  the  theory  of  incandescent 
mantles.  Rev.  Ge"n.  des  Sci.,  12  (1901),  pp.  358,  422. 

Wien. — Black  body  radiation  and  the  second  law  of  thermody- 
namics. Berl.  Ber.  (1893),  p.  55. — Temperature  and  entropy  of 
radiation.  Wied.  Ann.,  52  (1894),  p.  132. — The  upper  limit  of 
wave-lengths  in  the  radiation  of  solid  bodies,  etc.  Wied.  Ann., 
46  (1893),  p.  633;  52  (1894),  p.  150.— On  the  partition  of 
energy  in  the  emission  spectrum  of  a  black  body.  Wied.  Ann., 
58  (1896),  p.  662.— On  the  theory  of  radiation  from  a  black 
body.  Ann.  der  Phys.,  3,  1900,  p.  530;  Paris  Cong.  Rpts.,  2 
(1900),  p.  23. 

Wien  and  Lummer. — Method  of  demonstrating  the  radiation  law 
for  an  absolutely  black  body.  Wied.  Ann.,  56  (1895),  p.  451. 


BIBLIOGRAPHY.  327 

Beckmann. — Black  body  radiation,  etc.     Thesis,  Tubingen,  1898. 

Lummer. — On  the  gray  glow  and  red  glow.  Wied.  Ann.,  62  (1897),  p. 
13. — Radiation  from  black  bodies.  Paris  Cong.  Rpts.,  2 
(1900),  p.  56;  Arch.  Math.  Phys.  (3),  2  (1901),  p.  157;  3 
(1902),  p.  261. 

Lummer  and  Jahnke. — Ann.  der  Phys.,  3  (1900),  p.  283. 

Compau.— Radiation  laws,  etc.  Ann.  Chim.  Phys.  (7),  26  (1902), 
p.  488. 

Lummer  and  Pringsheim. —  The  radiation  from  a  black  body 
between  100°  and  1300°  C.  Wied.  Ann.,  63  (1897),  p.  395.— 
Distribution  of  energy  in  spectrum  of  black  body.  Verh. 
Deutsche  Phys.  Ges.,  1  (1899),  pp.  23  and  215.— Infra-red  radia- 
tion. Verb.  Deutsche  Phys.  Ges.,  2  (1900),  p.  163.— On  black 
radiation.  Ann.  der  Phys.,  6  (1901),  p.  192.— The  theoretical 
radiation  scale,  etc.,  at  2300°  absolute.  Verh.  Deutsche  Phys. 
Ges.  (5),  1  (1903),  p.  3. 

Lummer  and  Kurlbaum. — Electrically  treated  black  body  and  its 
temperature  measurement.  Verh.  Phys.  Ges.  (Berlin),  17 
(1898),  p.  106;  Ann.  der  Phys.,  5  (1901),  p.  829.— On  the 
change  of  photometric  intensity  in  the  temperature.  Verh. 
Deutsche  Phys.  Ges.,  2  (1900),  p.  89. 

Pringsheim. — Deduction  of  Kirchoff's  law.  Verh.  Deutsche  Phys. 
Ges.,  3  (1901),  p.  81. — Emission  from  gases.  Paris  Cong. 
Rpts.,  2,  1900. 

Bottomley.—  Radiation  from  solids.   Phil.  Mag.  (6),  4  (1902),  p.  560. 

Planck. — Entropy  and  temperature  of  radiant  heat,  etc.  Ann.  der 
Phys.,  1  (1900),  p.  719;  Sitzber.  Berl.  Akad.,  1  (1899),  p.  440.— 
On  irreversible  radiation.  Ann.  der  Phys.,  1  (1900),  p.  69. — 
On  a  bettering  of  Wien's  Spectral  Equation.  Verh.  deutsche 
Phys.  Ges.,  2  (1900),  p.  202. — Energy  distribution  hi  normal 
spectrum,  ibid.,  2  (1900),  p.  237. 

Raykigh.—Phtt.  Mag.  (5),  49  (1900),  p.  539;  (6)  1  (1901),  p.  93. 

Thiesen—  Verh.  Deutsche  Phys.  Ges.,  2  (1900),  p.  65. 

Rubens.—  Infra-red  radiation.     Wied.  Ann.,  69  (1899),  p.  576. 

Rubens  and  E.  Nichols.— Wied.  Ann.,  60  (1897),  p.  418. 

Rubens  and  Kurlbaum. — Berl.  Ber.  (1900),  p.  929;  Ann.  der  Phys., 
4  (1901),  p.  649;  Astrophys.  Jl.f  14  (1901),  p.  335. 

Maxwell. — Pressure  of  radiation.  Electricity  and  Magnetism, 
chap,  on  Electromagnetic  theory. 

Bartoli.— Wied.  Ann.,  22  (1884),  p.  31. 

Galttzine.— Wied.  Ann.,  47  (1892),  p.  479. 


328  BIBLIOGRAPHY. 

Pellat.—JL  de  Phys.,  July  1903. 

Lebedew. — Ann.   de  Phys.,  6  (1901),  p.  433;    Paris  Cong.  Rpt.,  2 

(1900),  p.  133. 
E.  F.  Nichols  and  Hull. — Phys.  Rev.,  1901  and  1903;   Astrophys. 

JL,  17  (1903),  p.  315. 

Rayleigh.—Phtt.  Mag.  (6),  3  (1902),  p.  338. 
Day  and  Van  Orstrand. — The  black  body  and  the  measurement  of 

extreme  temperatures.     Astrophys.  JL,  19  (1904),  p.  1. 
C.  Mendenhall  and  Saunders. — Astrophys.  JL,  13  (1901),  p.  25. 
Rasch. — On  the  photometric  determination  of  temperatures,  etc. 

Ann.  der  Phys.,  13  (1904),  p.  193. 
G.  W.  Stewart. — Spectral  energy  curves  of  black  body  at  room 

temperature.   Phys.  Rev.,  15  (1902),  p.  306;  17  (1903),  p.  476. 


HEAT-RADIATION  PYROMETER. 

Violk. — Solar  radiation.     Ann.  Chim.  et  Phys.,  5th  Series,  20  (1877), 

p.  289;  Jour,  de  Phys.  (1876),  p.  277. 
Rosetti.— Ann.  Chim.  et  Phys.,  17  (1879),  p.  177;    Phil.  Mag.,  18 

(1879),  p.  324. 

Deprez  and  d'Arsonval. — Societe"  de  Physique,  Feb.  5,  1886. 
Boys.— Radiomicrometer.     Phil.  Trans.,  180  (1887),  p.  159. 
Wilson  and  Gray. — Temperature   of  the   sun.     Phil.   Trans.,   185 

(1894),  p.  361. 
Langley. — Bolometer.     Am.  Jour,  of  Science,  21  (1881),  p.  187;  31 

(1886),  p.  1;  32  (1886),  p.  90;   (4),  5  (1898),  p.  241;    Jour,  de 

Phys.,  9,  p.  59. 
Terreschin. — Diss.  St.  Petersburg,  1898.     Jour.  Russ.  Phys.-chem. 

Ges.,  29  (1897),  pp.  22,  169,  277. 
Petravel—Proc.  Roy.  Soc.,  63  (1898),  p.  403;  Phil.  Trans.,  191 

(1898),  p.  501. 

Abbot. — Bolometer.     Astrophys.  Jour.,  8  (1898),  p.  250. 
Belloc—  Bolometer  errors.     L'e*clair.  elec.  (5),  15  (1898),  p.  383. 
Scheiner. — Radiation  and  temperature  of  sun  (Leipzig),  1899. 
Warburg. — Temperature  of  sun.     Verh.  D.  Ges.   (1),  2  (1899),  p. 

50. 
Fery. — The  measurement  of  high  temperatures  and  Stefan's  law. 

C.  R.,  134  (1902),  p.  977.    Jl.  de  Phys.,  Sept.  1904. 


BIBLIOGRAPHY.  329 


OPTICAL  PYROMETERS. 

See  also  laws  of  radiation  under  Lummer,  Pringsheim,  Kurlbaum, 
Wanner,  Wien,  and  Rasch. 

Kirchoff.—Awi.  Chim.  et  Phys.,  59  (1860),  p.  124. 

Ed.  Becquerel. — Optical  measurement  of  temperatures.  C.  R.,  55 
(1863),  p.  826.— Ann.  Chim.  et  Phys.,  68  (1863),  p.  49. 

Violle.— Radiation  from  platinum.  C.  R.,  88  (1879),  p.  171;  91 
(1881),  pp.  866,  1204. 

Kurlbaum  and  Schulze. — Pyrometric  examination  of  Nernst  lamps. 
Verh.  D.  Phys.  Ges.  (5),  24  (1903),  p.  125. 

D.  Berthelot. — On  a  new  optical  method,  etc.  Ann.  Chun,  et  Phys. 
(7),  26  (1902),  p.  58. 

Lummer. — Photometric  pyrometer.  Verh.  D.  Phys.  Ges.,  p.  131 
(1901). 

Schiitz. — Progress  in  pyrometry.  Verh.  Deutsche  Ing.,  48  (1904), 
p.  155. 

Fen/. — Temperature  of  the  arc.  C.  R.,  134  (1902),  p.  1201. — 
Absorption  Pyrometer.  Jl.  de  Phys.  (4),  3  (1904),  p.  32. 

Le  Chatelier  Pyrometer. — On  the  measurement  of  high  temperatures. 
C.  R.,  114,  pp.  214-216,  1892;  J.  de  Phys.  (3),  1,  pp.  185-205, 
1892;  Industrie  electrique,  April  1892.  —  On  the  temperature 
of  the  sun.  C.  R.,  114,  pp.  737-739,  1S92.— On  the  temperatures 
of  industrial  furnaces.  C.  R.,  114,  pp.  470-473, 1892;  Introduc- 
tion to  Metallurgy  (Roberts- Austen},  1903. — Discussion  of  Le 
Chatelier's  method:  (Violle)  C.  R.,  114,  p.  734,  1S92;  J.  de  Phys. 
(3),  p.  298,  1892;  (Becquerel)  C.  R.,  114,  pp.  225  and  390,  1892; 
(Le  Chatelier}  C.  R.,  114,  p.  340,  1892;  (Crova)  C.  R.,  114,  p. 
941,  1892.  Kayser's  Spectroscopy,  1902. 

Crova's  Pyrometer.  —  Spectrometric  study  of  certain  luminous 
sources.  C.  R.,  87,  pp.  322-325,  1878. — On  the  spectrometric 
measurement  of  high  temperatures.  C.  R.,  87,  pp.  979-981, 
1878. — Study  of  the  energy  of  radiations  emitted  by  calorific 
and  luminouseources.  Jour,  de  Phys.,  7,  pp.  357-363,  1878. — 
Spectrometric  measurement  of  high  temperatures.  Jour,  de 
Phys.,  9,  pp.  196-198,  1879;  C.  R.,  90,  pp.  252-254, 1880;  Ann. 
Chim.  et  Phys.  (5),  19,  pp.  472-550,  1880.— Photometric  com- 
parison of  luminous  sources  of  different  lines.  C.  R.,  93,  pp.  512 
-513,  1881.— Solar  photometry.  C.  R.,  95,  pp.  1271-1273, 1882. 


330  BIBLIOGRAPHY. 

End  of  Spectrum  Method. — A.  Crova.  Study  of  the  energy  of 
radiations  emitted  by  calorific  and  luminous  sources.  Jour, 
de  Phys.,  7  (1878),  pp.  357-363. 

W.  HempeL — On  the  measurement  of  high  temperatures  by  means 
of  a  spectral  apparatus.  Zs.  f.  Angewandte  Chem.,  14,  1901, 
pp.  237-242. 

Wanner  Pyrometer. — A.  Konig.  A  new  spectral  photometer. 
Wied.  Ann.,  53,  p.  785,  1894. — Description  of  Wanner  instru- 
ment. Iron  Age,  Feb.  18,  p.  24,  1904;  Phys.  Zs.,  3,  pp.  112-114, 
1902;  Stahl  und  Eisen,  22,  pp.  207-211,  1902;  Zs.  Vereines 
Deut.  Ing.,  48,  pp.  160,  161,  1904.— (Wanner)  Photometric 
measurement  of  the  radiation  of  black  bodies.  Ann.  der  Phys., 
5,  pp.  141-155,  1900. — Martens  and  Grinbaum.  Improved 
form  of  Konig  spectrophotometer.  Ann.  der  Phys.,  5  (1903), 
p.  954. — Hase.  Measurements  with  Wanner  Pyrometer.  Zs. 
Anorg.  Chem.,  15  (1902),  p.  715. 

Holborn  and  Kurlbaum  Pyrometer. — Sitzber.  d.  k.  Akad  d.  Wis- 
sensch.  zu  Berlin,  June  13,  pp.  712-719  (1901);  Ann.  der  Phys., 
10  (1902),  p.  225. 

Morse  Pyrometer. — American  Machinist,  1903. 

Temperature  of  Flames.— Kurlbaum,  Phys.  Zs.,  3  (1902),  p.  187; 
Lummer  and  Pringsheim  (criticism  of  above),  Phys.  Zs.,  3 
(1902),  p.  233;  E.  W.  Stewart,  Phys.  Rev.,  1902,  1903;  Fcry,  C. 
R.,  137  (1903),  p.  909;  Haber  and  Richardt,  Zs.  Anorg.  Chem., 
38  (1904),  p.  5. 

Waidner  and  Burgess.— Bull.  Bureau  of  Standards,  1,  No.  2  (1904). 


EXPANSION-  AND  CONTRACTION-PYROMETERS. 

Wedgwood.— Phil.  Trans.,  72  (1782),  p.  305;  74  (1784),  p.  358. 

Weinhold.— Pogg.  Ann.,  149  (1873),  p.  186. 

Boh—  Die  Pyrometer,  Berlin,  1888. 

Guyton  and  Morveau. — Ann.  Chim.  et  Phys.,  1st  Series,  46  (1803), 

p.  276;  73  (1810),  p.  254;  74  (1810),  pp.  18, 129;  90  (1814),  pp. 

113,  225. 
J.  Joly. — The  meldometer.     Proc.  Roy.  Irish  Academy,  3d  Series, 

2  (1891),  p.  38. 

Ramsay  and  Eumorfopoulos. — Phil.  Mag.,  41  (1896),  p.  360. 
High-range    Mercury    Thermometers. — Weber,    Ber.    Be  lin   Akad., 

Dec.  1903;   Wiebe,  Ibid.,  July  1884,  Nov.  1885;  Zs.  Tnstr  kund^, 


BIBLIOGRAPHY.  331 

6  (1886),  p.  167;   8  (1888),  p.  373;  10  (1890),  p.  207;  .Schott, 
ibid.,  11  (1891),  p.  330. 

Quartz  Thermometers. — Dufour,  C.  R.,  188  (1900),  p.  775;   Sicbert, 
Zs.  Elektroch.  (Ha  le),  10,  p.  26. 


FUSIBLE-CONE  PYROMETER. 

Lauth  and  Vogt. — Pyrometric  measurements.     Bull.  Soc.  Chim.,  46 

(1886),  p.  786. 
Seger—  Thorindustrie  Zeitung,  1885,  p.  121;  1886,  pp.  135,  229. 


PYROMETERS  BASED  ON  FLOW  OF  FLUIDS. 

A.  Job. — Viscosity  pyrometer.     C.  R.,  134  (1902),  p.  39. 

Uhling  and  Steinbart.—Sthal  u.  Eisen,  1899. 

Carnelly  and  Burton. — Water  circulation.     Jl.  Chem.  Soc.  (Lond.), 

45  (1884),  p.  237.      Also  described  in  Sir    Roberts-Austen's 

Metallurgy,  1902. 
Barus.— Bull.  54,  Geolog.  Survey,  1889. 


RECORDING-PYROMETERS. 

Le  Chatelier—  Study  of  clays.     C.  R.,  104  (1887),  p.  1443. 
Roberts-Austen. — First  Report  of  the  Alloys  Research  Committee, 

Proc.  Inst.  Mech.  Engrs.  (1891),   p.   543;   Nature,  45   (1892); 

B.  A.  Report   (1891);   Jour,  of  Soc.  of  Chem.  Industry,  46 

(1896),  p.  1;  Proc.  Inst.  Mech.  Eng.  (1895),  p.  269;    (1897), 

pp.  67,  243;  Proc.  Roy.  Soc.,  49  (1891),  p.  347. 
G.  Charpy. — Study  of  the  tempering  of  steel.     Bull,  de  la  Soc, 

d'encouragement,  4th  Series,  10  (1895),  p.  666. 
Callendar. — Platinum  recording-pyrometer.     Engineering,  May  26, 

1899,  p.  675. 
Stansfield.— Phil.  Mag.  (5),  46  (1898),  p.  59;    Phys.  Soc.  London, 

16  (2),  (1898),  p.  103. 

Bristol. — Air-pyrometer.     Eng.  News,  Dec.  13,  1900. 
Saladin—  Iron  and  Steel  Metall.  and  Metallog.,  Jan.  1904. 


332  BIBLIOGRAPHY. 


FUSING-  AND  BOILING-POINTS. 

FUSION. 

Prinsep.—Airn.  Chim.  et  Phys.,  2d  Series,  41  (1829),  p.  247. 
Lauth.— Bull.  Soc.  Chim.  Paris,  46  (1886),  p.  786. 
E.  Becq-uerel.—Aim.  Chim.  et  Phys.,  3d  Series,  68  (1863),  p.  497. 
Violle.—C.  R.,  85  (1877),  p.  543;   87  (1878),  p.  981;  89  (1879),  p. 

702. 
Holborn  and  Wien.—Wied.  Ann.,  47  (1892),  p.  107;   56  (1895),  p. 

360;  also  Zeits.  fur  Instrumentenk.  (1892),  p.  257. 
Holborn  and  Day. — Drude's  Ann.,  4,  1  (1901),  p.  99,  and  Am.  Jour. 

of  Sci.,  11  (1901),  p.  145.— Wied.  Ann.,  68  (1899),  p.  817,  and 

Am.  Jour,  of  Sci.  (4),  8  (1899),  p.  165. 
Ehrhardt  and  Schertel. — Jahrb.  fur  das  Berg-  und  Hiittenw.  im  K. 

Sachseri  (1879),  p.  154. 
Ledeboer.— Wied.  Beib.,  5  (1881),  p.  650. 
Van  der  Weyde.—1879,  see  Carnelly's  Tables. 
Calkndar.— Phil.  Mag.,  5th  Series,  47  (1899),  p.  191;  48,  p.  519. 
Curie. — Ann.  de  Chim.  et  de  Phys.,  5th  Series,  5  (1895). 
Barus. — Bull.  54,  U.  S.  Geological  Survey  (1889),  and  Behandlung 

u.  Messung  hoher  Temp.  Leipzig  (1892);  Am.  Jour,  of  Sci.,  3d 

Series,  48  (1894).,  p.  332. 
Berthelot.—C.  R.,  126,  Feb.  1898. 
Le  Chatelier.—C.  R.,  114  (1892),  p.  470. 
V.  Meyer,  Riddle  and  Lamb. — Chem.   Ber.,  27    (1894),  p.  3129. 

(Salts.) 
MoUenke. — Zeits.  fur  Instrumentenk.,  19  (1898),  p.  153.     (Iron  and 

Steel.) 

Cusack.— Proc.  Roy.  Irish  Acad.,  3d  Series,  4  (1899),  p.  399. 
Landolt  and  Bbrnstein. — Phys.  Chem.  Tabellen,  Berlin,  1894. 
Carnelly. — Melting  and  Boiling  Point  Tables,  London,  1885. 
Holman,  Lawrence  and  Barr. — Phil.  Mag.  (5),  42  (1896),  p.  37,  and 

Proc.  Am.  Acad.,  31,  p.  218. 
Heycock  and  Neville. — Phil.  Trans.,  189,  p.  25;   Jour.  Chem.  Soc., 

71  (1897),  p.  333;  Nature,  55  (1897),  p.  502;  Chem.  News,  75 

(1897),  p.  160. 

Heraeus—  Manganese.     Zs.  Elecktroch.,  8  (1902),  p.  185. 
Nernst.—Zs.  Elektrotech.,  1903. 
Rasch.— Ann.  d.  Phys.,  1904. 


BIBLIOGRAPHY.  333 

D.  Berthelot.— Ann.  Chim.  et  Phys.,  1902.— Gold.  C.  R.,  138  (1904), 

p.  1153. 
Richards. — Application  of  phase  rule  to  Cu,  Ag,  Au.    Am.  Jl.  ScL 

(4),  13  (1902),  p.  377. 
Jacquerod  and  Perrot.—Gold.     C.  R.,  138  (1904),  p.  1032. 

EBULLITION. 

Barus. — L.  C.  (under  Fusion),  and  Am.  Jour.  (5),  48  (1894),  p.  332. 

Troost.— C.  R.,  94  (1882),  p.  788;  94  (1882),  p.  1508;  95  (1882),  p. 
30. 

Le  Chatelier. — C.  R.,  121  (1895),  p.  323.  (See  also  under  Thermo- 
electric Pyrometer.) 

Berthelot. — Seances  de  la  soc.  de  physique,  Paris,  Feb.  1898,  and 
Bull,  du  Museum,  No.  6  (1898),  p.  301. 

Callendar  and  Griffiths. — Proc.  Roy.  Soc.  London,  49  (1891),  p.  56. 

Chappuis  and  Harker. — Travaux  et  Me*m.  du  Bureau  Int.  des 
Poids  et  des  Mesures,  12, 1900;  Phil.  Trans.,  1900. 

Preyer  and  V.  Meyer.— Zeits.  fur  Anorg.  Chem.,  2  (1892),  p.  1;  Berl. 
Ber.,  25(1892),  p.  622. 

S.  Young. — Trans.  Chem.  Soc.  (1891),  p.  629. 

MacCrae.— Wied.  Ann.,  55  (1895),  p.  95. 

Callendar.— Phil.  Mag.  (5),  48  (1899),  p.  519.     (Fusion  also.) 

D.  Berthelot. — Ann.  Chim.  et  Phys.,  1902. 

Fery. — Cu  and  Zn.     Ann.  Chun,  et  Phys.  (7),  28  (1903),  p.  428. 

R.  Rothe—  Sulphur.     Zs.  Instrumk.,  23,  p.  364  (1903). 


PYROMETRIC  MATERIALS. 

PORCELAIN  I      EXPANSION. 

Deville  and  Troost.— C.  R.,  57  (1863),  p.  867. 

Bedford— ft.  A.  Report,  1899. 

Benoit. — Trav.  etMem.  du  Bureau  Int.,  6,  p.  190. 

Tutton.— Phil.  Mag.  (6),  3  (1902),  p.  631. 

Chappuis.— Phil.  Mag.  (6),  3  (1902),  p.  243. 

HoWorn  and  Day.— Aim.  der  Phys.  (4),  2  (1900),  p.  505. 

Holborn  and  Gruniesen. — Ann.  der  Phys.  (4),  6  (1901),  p.  136. 


334  BIBLIOGRAPHY. 


METALS:  EXPANSION. 

Holborn  and  Day. — Ann.  der  Phys.,  4  (1901),  p.  104;  Am.  Jl.  Sci. 

(4),  11  (1901),  p.  374. 
Le  Chatelier.—C.  R.,  128  (1899),  p.  1444;   129,  p.  331;  107  (1888), 

p.  862;  108  (1896),  p.  1046;  111  (1890),  p.  123. 
Charpy  and  Grenet.—C.  R.,  134  (1902),  p.  540. 
Terneden. — Thesis,  Rotterdam,  1901  (Fortsch.  der  Phys.,  1901). 
Dittenberger.—Zs.  Ver.  Deutsche  Ingen.,  46  (1902),  p.  1532. 

QUARTZ. 

Le  Chatelier.—C.  R.,  107  (1888),  p.  862;  108,  p.  1046;  130,  p.  1703. 

Callendar. — Chem.  News,  83  (1901),  p.  151. 

Holborn  and  Henning. — Ann.  der  Phys.,  4  (1903),  p.  446. 

Scheel— Deutsch.  Phys.  Ges.  (5),  5  (1903),  p.   119.— Verh.  Phys. 

Tech.  Reichsanstalt,  1904. 
Shenstone. — Properties  of  Amorphous  Quartz.     Nature,  64  (1901), 

pp.  65  and  126,  contains  history  to  date. 
Dufour. — Tin-quartz  thermometer.     C.  R.,  130,  p.  775. 
Villard.— Permeability  for  H  at  1000°  C.     C.  R.,  130,  p.  1752. 
Joly. — Plasticity,  etc.     Nature,  64  (1901),  p.  102. 
Moissan  and  Siemens. — Action  of  water  on.     C.  R.,  138  (1904),  p. 

939. — Solubility  in  Zn  and  Pb.   C.  R.,  138  (1904),  p.  86. — Vapor 

pressure  of.     C.  R.,  138  (1904),  p.  243. 
Heraeus. — Properties:     a    general    summary.       Zs.    Elektroch.,  9 

(1903),  p.  848. 
Brun. — Fusion.     Arch.  Sc.  Phys.  Nat.  (Geneva)  (4),  13  (1902),  p. 

313. 
Hititon. — Lamps,  etc.     Am.  Electroch.  Soc.,  Sept.  1903. 

GLASS:  EXPANSION. 

Holborn  and  Gruniesen. — Ann.  der  Phys.  (4),  6  (1901),  p.  136. 
Bottomley  and  Evans. — Phil.  Mag.,  1  (1901),  p.  125. 

VARIOUS  SUBJECTS. 

Le  Chatelier. — Specific  heat  of  carbon.     C.  R.,  116  (1893),  p.  1051; 

Soc.  Franc,  de  Phys.,  No.  107  (1898),  p.  3. 
Barus. — Bull,  of  U.  S.  Geological  Survey  No.  54,  1889.      (Pyrom- 

etry.)     Report  on  the  progress  of  pyrometry  to  the  Paris  Con- 


BIBLIOGRAPHY.  335 

gress,  1900.     (This  is  the  latest  and  best  summary  of  pyrometric 

methods  to  date.) — Viscosity  and  temperature.     Wied.  Ann., 

96  (1899),  p.  358;   and  Callmdar,  Nature,  49  (1899),  p.  494.— 

Long-range   temperature   and   pressure   variables   in   physics. 

Nature,  56  (1897),  p.  528. 
Baly  and  Chorley. — Liquid-expansion  pyrometer.     Berl.   Ber.,  27 

(1894),  p.  470. 

Dufour.— Tin  in  quartz-pyrometer.     C.  R.,  180  (1900) ,  p.  775. 
Berihelot. — Interference  method  of  high-temperature  measurements. 

C.  R.,  120  (1895),  p.  831;  Jour,  de  Phys.  (3),  4  (1895),  p.  357; 

C.  R.,  Jan.  1898;  applications  in  C.  R.,  Feb.  1898. 
Moissan. — Le  four  electrique,  Paris,  1898.     Also  in  English. 
Fliegner. — Specific  heat  of  gases.     Wied.  Beibl.,  23  (1899),  p.  964. 
Topler. — Pressure-level  apparatus.     Wied.  Ann.,  56  (1895),  p.  609; 

57  (1896),  p.  311. 
Quincke. — An  acoustic  thermometer  for  high  and  low  temperatures. 

Wied.  Ann.,  63  (1897),  p.  66. 
K.  Scheel  — Ueber  Fernthermometer.     Veriag  v.  C.  Marhold,  Halle, 

1898.     48  pp. 
Heitmann. — Ueber  einen  neuen  Temperatur-Fernmessapparat  von 

Hartmann  und  Braun.     E.  T.  Z.,  19  (1898),  p.  355. 
Chree—  Recent  work  in  thermometry.     Nature,  58  (1898),  p.  304. 
Lemeray. — On  a  relation  between  the  dilation  and  the  fusing-pointe 

of  simple  metals.     C.  R.,  131  (1900),  p.  1291. 
Holborn  and  Austin. — Disintegration  of  the  platinum  metals  hi 

different  gases.     Phil.  Mag.  (6),  7  (1904),  p.  388. 
Stewart.— (Same  as  preceding.)     Phil.  Mag.  (5),  48  (1899),  p.  481. 
Hagen  and  Rubens. — On  some  relations  between  optical  and  electrical 

properties  of  metals.     Phil.  Mag.  (6),  7  (1904),  p.  157. 
KahJbaum. — On  the  distillation  of  metals.     Phys.  Zs.  (1900),  p.  32. 
Kahlbaum,  Roth,  and  Seidter.— (Ibid.)    Zs.  Anorg.  Ch.,  29  (1902), 

p.  177. 
j 

HOT-BLAST  PYROMETERS. 

(From  Sir  Roberts-Austen's  Metallurgy.) 

J.  Iron  and  Steel  Inst.,  (1884)  pp.  195,  240;  (1885)  p.  235;  (1886) 
p.  207;  (1888),  2,  p.  110.— Proc.  Inst.  M.  E.  (1852),  p.  53.— 
Jl.  Soc.  Chem.  Ind.,  (1885)  p.  40;  (1897)  p.  16. 

Wiborgh—  Industrial  Air  Pyrometer.  Jl.  Ir.  and  St.  Inst.,  2  (1888), 
p.  110. 


336 


Callendar.  —  Industrial  Air  Pyrometer.     Proc.  Roy.  Soc.,  50 

p.  247.  —  Measurement  of  extreme  temperatures.     Nature,  59, 
pp.  495  and  519  —  a  review  of  various  pyrometric  methods. 

Siebert.—Quntz  Thermometers.     Z*.  Elekiroch.  (Halle),  10,  p.  26. 

Mahlke.  —  On  a  comparison  apparatus  for  thermometers  between 
250°  and  600°  C.     Zs.  Instr.kunde,  14  (If  94),  p.  73. 

F.  Kraft.  —  Evaporation  and  boiling  of  metals  in  quartz  in  electric 
furnace.     Ber.  Deut.  Ch.  Ges.,  36,  p.  1690  (1903). 

CHEMICAL    DETERMINATIONS    OF   TEMPERATURES. 

Haber  and  Richardt.—The    water-gas   equilibrium  in  the  Bunsen 

flame,  and  the  chemical  determination  of  high  temperatures. 

Zs.  Anorg.  Cheni.,  38  (1904),  p.  5. 
Zenghelis.  —  Chemical    reactions   at  very    high    temperatures.     Zs. 

Phys.  Chem.,  4G  (1903),  p.  287. 
Nemst.  —  On  the  determination  of  high  temperatures.     Phys.  Zs.,  4 

(1903),  p.  733. 

RESISTANCE   FURNACES. 

A.  Kaldhne.  —  On  electric  resistance  furnaces.     Ann.  d.  Phys.,  11, 
p.  257  (1903). 

E.  Haagen.  —  Platinum-foil  furnaces.    .Zs.  Elektroch.,  p.  509  (1902). 
W.    C.    Heraeus.  —  Electrical    laboratory  furnace.     Zs.  Elektroch., 

p.  201  (1902). 

C.  L.  Norton.  —  Laboratory  electric  furnaces.    Elec.  World  and  Eng., 

36,  p.  951  (1900). 

F.  A.  J.   Fitzgerald.  —  Principles   of    resistance    furnaces.     Trans. 

Am.  Elec.chem.  Soc.,  4,  p.  9;   Elec.chem.  Indus.,  2,  p.  242, 
1904. 

D.  Berthelot.-A.un.  Phys.  et  Chim.  (1902,  I.e.). 
Holborn  and  Day.  —  Ann.  der  Phys.  (1901,  1.  c.). 

Doelter.  —  Two  electric  furnaces  for  melting-points.     Centralbl.  f. 
Min.  (1902),  p.  426. 


INDEX. 


Abbot,  197,  198 
Actinometer,  190 
Aging  of  lamp*,  241,  242 
Air-thermometer,  16,  17,  24,  31, 

36,  56,  103 

normal  thermometer,  36 
Aluminum,  freezing-point,  306 
Aniline,  boiling-point,  307 
Antimony,  freezing-point,  305 
Arnold,  167 
Avenarius,  121,  153 

Barr,  163 

Barus,  7,  53,  80,  155,  157,  269, 

29^,  315 

gas-pyrometer,  75 
thermoelectric  pyrometer,  ITS, 

134,  15S 
Beckmann,  1^3 
Bevjuerel,   16,   50,   51,   64,   135, 

20^,  29S,  299,  300 
gas-pyrometer,  69 
thermoelectric  pyrometer,  120, 

121 

Bedford,  53 
Bell,  Sir  Lothian,  291 
Benoit,  51 
Benzophenone,        boiling-point, 

307 

Berthelot,  94 
D.  Berthelot,  8,  ?5,  33,  34,  164, 

298,  299,  300 
interference      gas-pyrometer, 

86,  314,  315 
Biju-Duval,  93,  97 
Black  body,  173,  176,  231,  315 


Bolometer,  197,  276 

Boltzmann,  178,  182,  199,  313 

Boudouard,  219 

Boys,  194 

Brit.  Assoc.  Rpt.  on  platinum- 

thermometry,  102 
Bureau,    International,    20,    22, 

26,  36,  110 
Bureau  of  Standards,  309 

Calendar,  7,  26,  29,  31,  32,  34, 
35,  42,  110,  114,  269,  296, 
29\315 

electric- resistance  pyrometer, 
102,  104,  105,  106;il2,  273, 
276,  277 

gas-thermometer,  42 
Calorimeters,  94 
Berthelot,  94 
jacketed,  95 
Siemens,  97 

Calorimetric  pyrometer,  9,  91 
calorimeters',  94 
choice  of  metal,  92 
conditions  of  use,  99 
precision  of,  97 
Carnetty  and  Burton,  268 
Cell,  standard,  128 
West  on,  129 
Carhart-Clark,  129 
Chappuis,  20,  21,  22,  24,  26,  31, 
32,  34,  40,  45,  50,  53,  54, 
110,  296 

Charpy,  167,  284,  285 
Cobalt  glass,  use  of,  246 
Compeaux,  52 

337 


838 


INDEX. 


Conclusion,  312 
Contraction-pyrometer,  11,  253 
Copper,   freezing-point   of,   301, 

304 

Cornu,  210 
Corrections  to: 

constant-pressure    thermome- 
ter, 62 

constant -volume     thermome- 
ter, 56 
voluminometer   thermometer, 

64 
Crafts,  7,  23,  52,  61,  63,  82,  86, 

113,  296 
Crova,  186 

pyrometer  of,  249 

Day,  8,  48,  50,  53,  54,  77,  79, 
155,  163,  164,  167,  297,  298, 
299,  300,  301,  315 

Dickson,  108 

Dilution-pyrometers,  268 

Dufour,  260 

Dulong  and  Petit,  177,  191,  192, 
193 

Electric  heating,  163,  310 
Electric-resistance      pyrometer, 

10,  101 

as  a  standard,  110 
conditions  of  use,  119 
experimental    arrangements, 

110 

formula?  for,  102,  106 
law  of,  104 
nomenclature,  106 
recording,  273 
results  with,  112 
sources  of  error,  114 

changes  in  constants,  118 
compensation,  114 
heating  of,  114 
insulation,  114 
lag,  114 
Emissive  powers,  172,  204,  206, 

214 
Energy  distribution,  laws  of,  179 

curves,  181 
Euchene,  93 
Expansion  coefficients : 
of  gases,  17,  68 


Expansion  coefficients: 

of  glass,  54 

of  iron,  51 

of  platinum,  50 

of  porcelain,  53,  54,  76 

of  quartz,  55 
Expansion-pyrometers,  253,  256 

Joly  meldometer,  257 

high-range  thermometers,  259 
Eye  estimation  of  temperatures, 
245 

Fcry,  244,  245 

absorption-pyrometer,  226 
thermoelectric  telescope,  198, 

201 

Fixed  points,  6,  8,  68,  69,  70,  74, 
76,   89,  90,   112,   113,   156, 
295,  303,  307,  308 
Furnaces: 

Barus  rotating,  75 
electric  resistance,  310 
iridium,  311 
Fusible  cones,  11,  262 
Fusing-point,  pyrometry,  261 

Gasparin,  188 

Gas-scale,  4,  17 

Gas-thermometers,  9,  13,  17,  22, 

48 
at  constant  pressure,  14,  42, 

62 

at  constant  volume,  13,  36,  56 
compensated  form,  42,  63 
correction  to  normal  scale,  32 
for  high  temperatures,  47,  79 
indirect  processes,  82 
industrial,  SI 
of  Barus,  75 
of  Becquerel,  69 
of  Berthelot,  86 
of  Deville  and  Troost,  69 
of  Holborn  and  Day,  77 
of  Holborn  and  Wien,  76 
of  Jacquerod  and  Perrot,  79 
of  Mallard  and  Le  Chatelier,  74 
of  Pouillet,  66 
of  Viollc,  71 
recording,  271 
substance  of  bulb,  49 
volumetric,  15 


INDEX. 


339 


Gay-Lussac's  Law,  12 

Glass,  as  gas-thermometer  bulb, 

77 

exp?n?ion,  54 
Gold,  point  of  fusion,  298 
Griffiths,  7,  296,  315 

elect  rical- resist  ance     pyrome- 
ter, 102,  104,  105,  112 
Gruneisen,  53,  54 

Hadfield,  316 

Harker,  24,  26,  31,  34,  45,  105, 
110,  296 

Heat-radiation  pyrometer,  187 
conditions  of  use,  198 
of  Fery,  198 

Hempel,  186 

Henning,  55 

Heraeus,  54,  55,  152.  164,  168, 
169,  170,  311 

Haycock,  5,  113,  118,  297,  300, 
301,  313 

Holborn,  7,  8,  48,  50,  52,  53,  54, 
55,  72,  76,  77,  79,  103,  108, 
135,  141,  154,  155,  163,  164, 
165,  167,  297,  29S,  299,  300, 
301,  302,  315 

Holborn  and  Kurlbaum  pyrome- 
ter, 237 

Holman,  132,  154,  163,  301,  313 

Howe,  167 

Hydrogen-thermometer,  18,  20, 
21 

International    Bureau.    20,    22, 

26,  36,  110 
Iridium,  freezing-point,  302 

-ruthenium  couple,  168 
Iron,  as  gas-thermometer  bulb,  5 

in  calorimeter-pyrometer,  92 

total  heat  of,  93 
Isochromatic  curves,  181 

Jacquerod,  79,  299,  300 

Job,  269 

Joly,  195,  257 

Joule  and  Thomson's  expt.,  30 

Kirchoff,  173,  175 

law  of,  204 
Kurlbaum,  175, 178,  244,  315 


Laboratories,  standardizing,  309 

Langky,  179,  197,  198,  277 

Lauth  and  Vogt,  262 

Lawrence,  163 

Le  Chatelier,  52,  64,  74,  76,  93, 
97,  140,  199,  219,  22!0,  226, 
229,  254,  314,315,316 
optical  pyrometer,  208 
adjustment  of,  212 
graduation,  216,  221 
measurements,  213,  216,  220 
modifications  of,  226 
precision  and  errors,  221 
the  photometer,  208 
recording  -  pyrometers,     278, 

291,  293 

thermoelectric  pyrometer, 
122,  134,  144,  153,  154,  167, 
278 

Lummer,  173,  178, 180, 184,  244, 
313,  315 

Mahlke,  260 
Mallard,  64,  74 
Mariolte's  Law,  12 
Mascart,  285 
Meier,  82,  86 
Meldometer,  195,  257 
Mercury-thermometers,  16,  259 
Mesurt  xad  Nouel,  247 
Moissan,  55,  314,  315 
Monochromatic  glasses,  211 
Mylius,  55 

Naphthaline,  boiling-point,  307 

National  Bureau  of  Standards, 
309 

National    Physical    Laboratory, 
105,  309* 

Nernst,  302,  311,  314,  315 

Neville,  7,  113,  118,  297,  300, 
301,  313 

Newton,  177,  191,  192,  193 

Nichols,  243 

Nickel,  in   calorimeter-pyrome- 
ter, 93 
total  heat  of,  94 

Nitrogen-thermometer,    18,   20, 

21,  25 
compared  with  platinum,  105 

Normal  thermometer,  22,  36 


340 


INDEX. 


Optical  pyrometer,  10,  204 

conditions  of  use,  242 

of  Crova,  249 

of  Fery,  226 

of    Holborn    and    Kurlbaum, 
237 

of  Le  Chatelier,  208 

of  Mesure  and  Nouel,  247 

of  Morse,  241 

of  Wanner,  226,  229 
Osmond,  167 

Palladium,  specific  heat  of,  73 
thermoelectric  properties,  121, 
122 

Paschen,  178,  183,  313 

Perrot,  79,  299,  300 

Pionchon,  93 

Planck,  Law  of,  183,  313 

Platinum,    as    gas-thermometer 

bulb,  36,  49,  67,  78 
as  resistance-thermometer, 101 
fusing-point  of,  72,  302 
in  calorimeter-pyrometer,  92 
specific  heat  of,  71,  92 
thermoelectric  properties,  121 
total  heat  of,  92 

Porcelain,   as    gas-thermometer 

bulb,  51,  77 
expansion  of,  53,  54,  76 

Pouillet,   13,    16,  92,   135,   188, 

191,  299,  300 
gas-thermometer,  66 
thermoelectric  pyrometer,  120 

Pringsheim,  178,  180,  184,  244 

Pyrometers,  standardization  of, 

295 
types  of,  9 

Pyrrh6liometre,  188 

Quartz,      as      gas-thermometer 

bulb,  77 
expansion  of,  55 

"Radiation,  laws  of,  171,  177 
and  temperature,  171 
application  to  pyrometry,  185, 

187 

measurement  of,  207,  245 
Radiation-pyrometer,  9, 187, 198 
of  Fe*ry,  198 


Radiomicrometer,  194 
Rankine,  17 
Rasch,  172,  302 
Recording-pyrometers,  271 
electrical  resistance,  273 
gas,  271 
thermoelectric,  277,  291 

continuous,  282 

discontinuous,  279 
Regnault,  7,  13,  16,  17,  18,  63, 

83,  84,  89,  92,  113,  296 
Reichsanstalt,    7,    50,    77,    105, 

133,  141,309,313,315 
Richards,  301 
Roberts-Austen,  150,163,167, 285, 

287,  288,  289,  290,  291,  316 
recording-pyrometers,  282 
Rose-Innes,  34 
Rosetti,  177,  191,  194,  196 
Roux,  283 
Rubens,  183 

Sainte-Claire-Deville,  16,  50,  51, 
69,  71,82,83,84,  298 

gas-pyrometer,  69 
Saladin,  291,  293 
Salts,  fusing-points  of,  307 
Scheel,  55 
Secchi,  191 
Seger,  262,  316 

Selenium,  action  of  light  on,  252 
Shenstone,  55 
Siebert  and  Kuhn,  54,  260 
Siemens,  316 

calorimeter,  97 

electrical  pyrometer,  101 
Silver,  fusing-point  of,  300 
Standardization  of  pyrometers, 
295,  308 

fixed  points,  295,  308 

laboratories  for,  309 
Standards,  Bureau  of,  309 
Stansfield,  155,  163,  297,  301 
Stefan,  Law  of,  177, 186, 188, 196 
197,  198,  199,  201,  203,  315 
Stewart,  244 
Sulphur,  boiling-point,  296 

Tail,  121,  153 

Temperature     (see    also    Fixed 
points) 


INDEX. 


341 


Temperature  and  radiation,  171 

definition  of,  2 

normal  scale  of,  12,  22 

of  a  "black  body,"  176 

of  flames,  243 

of   industrial   processes,   etc., 
167,  220,  221 

of  sun,  189,  191,  194,  220 
Thermodynamic  scale,  12,  26 

and  gas-scale,  26 

calculation  of  corrections,  33 
Thermoelectric    pyrometer,    10, 
76,  120 

arrangement  of  wires,  146 

chemical  changes,  126 

choice  of  couple,  124 

cold  junction,  151 

conditions  of  use,  163 

effect  of  heating,  166 

electromotive  force,  124 

formulae,  121,  153 

galvanometers  for,  135 

graduation,  152 

heterogeneity  of  wires,  122 

industrial  applications,  167 

industrial    practice,    require- 
ments of,  144 

insulation  and  protection,  147 

iridium-ruthenium,  168 

junction  of  wires,  146 

methods  of  measurement,  126 

parasite  currents,  126 

principle  of,  10,  76,  120 

recent  researches,  162 

resistance  of  couples,  133 
Thermometric  scales,  3,  12,  26, 
106 

accuracy  of,  9 

normal  scale,  22,  25 

N  and  H  scale  differences,  21 


Thermometric  scales,  platinum 

vs.  gas,  105 
Thermophones,  267 
Transpiration-pyrometers,  268 
Troost,  69,  82,  86 
Tutton,  53 
Tyndall,  177 

Uhling  and  Steinbart,  270 

ViUard,  55 

Viotte,  6,  23,  72,  92,  190,  191 , 
298,  299,  300,  302 

gas-pyrometer,  71 
Viscosity-pyrometer,  269 
Volumetric  thermometer,  15 

corrections  to,  64 

Waidner  and  Burgess,  185,  221, 

232,  236 

Wanner  pyrometer,  226,  229 
description    and    calibration, 

229 

range  and  limitations,  235 
sources  of  error,  232 
Water,  boiling-point,  307 
Wedgwood,  1,  253,  254,  255,  316 

pyrometer,  1,  253 
Whipple,  112 

Wiborgh,  industrial  air-pyrome- 
ter, 81 

thermophones,  267 
Wien,  8,  52,  72,  76, 103, 108, 135, 

141,  154,  173,  299 
laws  of,   181,   182,   183,  184, 
186,  198,  221,  231,  238,  300, 
302,  313,  315 
Wilson  and  Gray,  194,  196,  220 

Zinc,  boiling-point,  297 
fusing-point,  297 


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*  Dudley's  Military  Law  and  the  Procedure  of  Courts-martial..  .  Large  12010,  2  50 
Durand's  Resistance  and  Propulsion  of  Ships 8vo,  5  oo 

2 


*  Dyer's  Handbook  of  Light  Artillery I2mo,  3  oo 

Eissler's  Modern  High  Explosives 1 8vo,  4  oo 

*  Fiebeger's  Text-book  on  Field  Fortification Large  i2mo,  2  oo 

Hamilton  and  Bond's  The  Gunner's  Catechism i8mo,  i  oo 

*  Hofrs  Elementary  Naval  Tactics 8vo,  i  50* 

Ingalis's  Handbook  of  Problems  in  Direct  Fire 8vo,  4  oo 

*  Lissak's  Ordnance  and  Gunnery 8vo,  6  oo 

*  Ludlow's  Logarithmic  and  Trigonometric  Tables 8vo,  i  oo 

*  Lyons's  Treatise  on  Electromagnetic  Phenomena.  Vols.  I.  and  II..8vo,  each,  6  oo 

*  Mahan's  Permanent  Fortifications.    (Mercur.) 8vo,  half  mor.  7  50 

Manual  for  Courts-martial i6mo,  mor.  i  50 

*  Mercur's  Attack  of  Fortified  Places i2mo,  2  oo 

*  Elements  of  the  Art  of  War 8vo,  4  oo 

Metcalf's  Cost  of  Manufactures — And  the  Administration  of  Workshops.  .8vo,  5  oo 

*  Ordnance  and  Gunnery.     2  vols Text  12010,  Plates  atlas  form  5  oo 

Nixon's  Adjutants'  ManuaL 24010,  i  oo 

Peabody's  Naval  Architecture 8vo,  7  50 

*  Phelps's  Practical  Marine  Surveying 8vo,  2  50 

Powell's  Army  Officer's  Examiner i2mo,  4  oo 

Sharpe's  Art  of  Subsisting  Annies  in  War i8mo,  mor.  i  50 

*  Tupes  and  Poole's  Manual  of  Bayonet  Exercises  and    Musketry  Fencing. 

24010,  leather,  50 

*  Weaver's  Military  Explosives 8vo,  3  oo 

Woodhull's  Notes  on  Military  Hygiene iomo,  i  50 


ASSAYING. 

Betts's  Lead  Refining  by  Electrolysis 8vo,  4  oo 

Fletcher's  Practical  Instructions  in  Quantitative  Assaying  with  the  Blowpipe. 

i6mo,  mor.  i  50 

Furman's  Manual  of  Practical  Assaying 8vo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments.  .  .  .8vo,  3  oo 

Low's  Technical  Methods  of  Ore  Analysis 8vo,  3  oo 

Miller's  Cyanide  Process I2mo,  i  oo 

Manual  of  Assaying 12010,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) 12010,  2  50 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Ricketts  and  Miller's  Notes  on  Assaying 8vo,  3  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 

Wilson's  Chlorination  Process I2mo,  I  50 

Cyanide  Processes i2mo,  i  50 


ASTRONOMY. 

Comstock's  Field  Astronomy  for  Engineers 8vo,  2  50 

Craig's  Azimuth 4to,  3  50 

Crandall's  Text-book  on  Geodesy  and  Least  Squares 8vo,  3  oo 

Doolittle's  Treatise  on  Practical  Astronomy . 8vo,  4  oo 

Gore's  Elements  of  Geodesy 8vo,  2  50 

Hayford's  Text-book  of  Geodetic  Astronomy.  . 8vo,  3  oo 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy. 8vo,  2  50 

*  Michie  and  Harlow's  Practical  Astronomy 8vo,  3  oo 

Rust's  Ex-meridian  Altitude,  Azimuth  and  Star-Finding  Tables.     (In  Press.) 

*  White's  Elements  of  Theoretical  and  Descriptive  Astronomy 12010,  2  oo 


CHEMISTRY. 

Abderhalden's  Physiological  Chemistry  in  Thirty  Lectures.     (Hall  and  Defren). 
(In  Press.) 

*  Abegg's  Theory  of  Electrolytic  Dissociation,    (von  Ende.) I2mo,  I  25 

Adriance's  Laboratory  Calculations  and  Specific  Gravity  Tables i2mo,  i  25 

Alexeyeff ' s  General  Principles  of  Organic  Syntheses.     (Matthews.) 8vo,  3  oo 

Allen's  Tables  for  Iron  Analysis 8vo,  3  oo 

Arnold's  Compendium  of  Chemistry.     (Mandel.) Large  i2mo,  3  50 

Association    of  State  and  National  Food  and  Dairy  Departments,  Hartford 

Meeting,  1906 8vo,  3  oo 

Jamestown  Meeting,  1907 8vo,  3  oo 

Austen's  Notes  for  Chemical  Students i2mo,  i  50 

Baskerville's  Chemical  Elements.     (In  Preparation). 

Bernadou's  Smokeless  Powder. — Nitro-cellulose,  and  Theory  of  the  Cellulose 

Molecule i2mo,  2  50 

*  Blanchard's  Synthetic  Inorganic  Chemistry. I2mo,  i  oo 

*  Browning's  Introduction  to  the  Rarer  Elements 8vo,  i  50 

Brush  and  Penfield's  Manual  of  Determinative  Mineralogy 8vo,  4  oo 

*  Claassen's  Beet-sugar  Manufacture.     (Hall  and  Rolfe.) 8vo,  3  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.    (Boltwood.).  .8vo,  3  oo 

Cohn's  Indicators  and  Test-papers i2mo,  2  oo 

Tests  and  Reagents 8vo,  3  oo 

*  Danneel's  Electrochemistry.     (Merriam.) i2mo,  i  25 

Duhem's  Thermodynamics  and  Chemistry.     (Burgess.) 8vo,  4  oo 

Eakle's  Mineral  Tables  for  the  Determination  of  Minerals  by  their  Physical 

Properties 8vo,  i  25 

Eissler's  Modern  High  Explosives 8vo,  4  oo 

Effront's  Enzymes  and  their  Applications.     (Prescott.) 8vo,  3  oo 

Erdmann's  Introduction  to  Chemical  Preparations.     (Dunlap.) i2mo,  i  25 

*  Fischer's  Physiology  of  Alimentation Large  I2mo,  2  oo 

Fletcher's  Practical  Instructions  in  Quantitative  Assaying  with  the  Blowpipe. 

i2mo,  mor.  i  50 

Fowler's  Sewage  Works  Analyses i2mo,  2  oo 

Fresenius's  Manual  of  Qualitative  Chemical  Analysis.     (Wells.) 8vo,  5  oo 

Manual  of  Qualitative  Chemical  Analysis.  Part  I.  Descriptive.  (Wells.)  8vo,  3  oo 

Quantitative  Chemical  Analysis.     (Cohn.)     2  vols 8vo,  12  50 

When  Sold  Separately,  Vol.  I,  $6.     Vol.  II,  $8. 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Furman's  Manual  of  Practical  Assaying 8vo,  3  oo 

*  Getman's  Exercises  in  Physical  Chemistry I2mo5  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers I2mo,  i  23 

*  Gooch  and  Browning's  Outlines  of  Qualitative  Chemical  Analysis. 

Large  i2mo,-  i  25 

Grotenfelt's  Principles  of  Modern  Dairy  Practice.     (Woll.) i2mo,  2  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) i2mo,  i  25 

Hammarsten's  Text-book  of  Physiological  Chemistry.     (Mandel.) 8vo,  4  oo 

Hanausek's  Microscopy  of  Technical  Products.     (Winton. ) Svo,  5  oo 

*  Haskins  and  Macleod's  Organic  Chemistry i2mo,  2  oo 

Helm's  Principles  of  Mathematical  Chemistry.     (Morgan.) I2mo,  i  50 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  mor.  2  50 

*  Herrick's  Denatured  or  Industrial  Alcohol Svo,  4  oo 

Hinds's  Inorganic  Chemistry 8vo,  3  oo 

*  Laboratory  Manual  for  Students i2mo,  i  oo 

*  Holleman's    Laboratory   Manual    of    Organic    Chemistry  for   Beginners. 

(Walker.) i2mo,  i  oo 

Text-book  of  Inorganic  Chemistry.     (Cooper.) Svo,  2  50 

Text-book  of  Organic  Chemistry.     (Walker  and  Mott.) Svo,  2  50 

Holley  and  Ladd's  Analysis  of  Mixed  Paints,  Color  Pigments ,  and  Varnishes. 

Large  12  mo  2  50 
4 


Hopkins's  Oil-chemists'  Handbook 8vo,  3  oo 

Iddings's  Rock  Minerals 8vo,  5  oo 

Jackson's  Directions  for  Laboratory  Vv'ork  in  Physiological  Chemistry.  .8vo,  i  25 

Johannsen's  Determination  of  Rock-forming  Minerals  in  Thin  Sections..  .8vo,  4  oo 

Keep's  Cast  Iron 8vo,  2  50 

Ladd's  Manual  of  Quantitative  Chemical  Analysis I2mo,  i  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

*  JLangwurthy  and   Austen's   Occurrence   of  Aluminium  in  Vegetable  Prod- 

ucts, Animal  Products,  and  Natural  Waters 8vo,  2  oo 

Lassar-Cohri's  Application  of  Some  General  Reactions  to  Investigations  in 

Organic  Chemistry.  (Tingle.) i2mo,  i  oo 

Leach's  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control 8vo,  7  50 

Lob's  Electrochemistry  of  Organic  Compounds.  (Lorenz.) 8vo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments 8vo,  3  oo 

Low's  Technical  Method  of  Ore  Analysis 8vo,  3  oo 

Lunge's  Techno-chemical  Analysis.  (Cohn.) I2mo  i  oo 

*  McKay  and  Larsen's  Principles  and  Practice  of  Butter-making 8vo,  i  50 

Maire's  Modern  Pigments  and  their  Vehicles i2mo,  2  oo 

Mandel's  Handbook  for  Bio-chemical  Laboratory i2mo,  i  50 

*  Martin's  Laboratory  Guide  to  Qualitative  Analysis  with  the  Blowpipe .  .  i2mo,  60 
Mason's  Examination  of  Water.     (Chemical  and  Bacteriological.).  .  ..i2mo,  i  25 

Water-supply.     (Considered  Principally  from    a    Sanitary    Standpoint.) 

8vo,  4  oo 

Matthews's  The  Textile  Fibres.   2d  Edition,  Rewritten 8vo,  4  oo 

Meyer's  Determination  of  Radicles  in  Carbon  Compounds.     (Tingle.).  .I2mo,  i  oo 

Miller's  Cyanide  Process "mo,  i  oo 

Manual  of  Assaying i2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) .  .  .  .  i2mo,  2  50 

Mixter's  Elementary  Text-book  of  Chemistry I2mo,  i  50 

Morgan's  Elements  of  Physical  Chemistry I2mo,  3  co 

Outline  of  the  Theory  of  Solutions  and  its  Results I2mo,  i  oo 

*  Physical  Chemistry  for  Electrical  Engineers i2mo,  i  50 

Morse's  Calculations  used  in  Cane-sugar  Factories i6mo,  mor.  i  50 

*  Muir's  History  of  Chemical  Theories  and  Laws 8vo,  4  oo 

Mulliken's  General  Method  for  the  Identification  of  Pure  Organic  Compounds. 

VoL  I Large  8vo,  5  oo 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Ostwald's  Conversations  on  Chemistry.     Part  One.     (Ramsey.) i2mo,  150 

"                   "               "           "             Part  Two.     (TurnbulL) i2mo,  2  oo 

*  Palmer's  Practical  Test  Book  of  Chemistry i2mo,  i  oo 

*  Pauli's  Physical  Chemistry  in  the  Service  of  Medicine.     (Fischer.) .  .  .  .  i2mo,  i   25 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

8vo,  paper,  50 
Tables  of  Minerals,  Including  the   Use   of  Minerals  and  Statistics  of 

Domestic  Production 8vo,  i  oo 

Pictet's  Alkaloids  and  their  Chemical  Constitution.     (Biddle.) 8vo,  5  oo 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oo 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis i2mo,  i  50 

*  Reisig's  Guide  to  Piece-dyeing 8vo,  25  oo 

Richards  and  Woodman's  Air,  Water,  and  Food  from  a  Sanitary  Standpoint.. 8vo,  2  oo 

Ricketts  and  Miller's  Notes  on  Assaying 8vo,  3  oo 

Rideal's  Disinfection  and  the  Preservation  of  Food 8vo,  4  oo 

Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  4  oo 

Riggs's  Elementary  Manual  for  the  Chemical  Laboratory 8vo,  i  25 

Robine  and  Lenglen's  Cyanide  Industry.  (Le  Clerc.) 8vo,  4  oo 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  oo 

Whys  in  Pharmacy J2mo,  i  oo 

5 


Ruer's  Elements  of  Metallography.     (Mathewson).     fin  Preparation.) 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Salkowski's  Physiological  and  Pathological  Chemistry.     (Orndorff.) 8vo,  2  50 

Schimpf  s  Essentials  of  Volumetric  Analysis lamo,  i  25 

*  Qualitative  Chemical  Analysis 8vo,  i  25 

Text-book  of  Volumetric  Analysis i2mo,  2  50 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students 8vo,  2  50 

Spencer's  Handbook  for  Cane  Sugar  Manufacturers i6mo,  mor.  3  oo 

Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  mor.  3  oo 

Stockbridge's  Rocks  and  Soils 8vo,  2  50 

*  Tillman's  Descriptive  General  Chemistry 8vo,  3  oo 

*  Elementary  Lessons  in  Heat 8vo,  i  50 

Treadwell's  Qualitative  Analysis.     (Hall.) 8vo,  3  oo 

Quantitative  Analysis.     (Hall.) 8vo,  4  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Van  Deventer's  Physical  Chemistry  for  Beginners.     (Bolrwood.) i2mo,  i  50 

Venable's  Methods  and  Devices  for  Bacterial  Treatment  of  Sewage 8vo,  3  oo 

Ward  and  Whipple's  Freshwater  Biology.     (In  Press.) 

Ware's  Beet-sugar  Manufacture  and  Refining.     Vol.  I Small  8vo,  4  oo 

Vol.  -II Small  8vo,  5  co 

Washington's  Manual  of  the  Chemical  Analysis  of  Rocks., 8vo,  2  oo 

*  Weaver's  Military  Explosives 8vo,  3  oo 

Wells's  Laboratory  Guide  in  Qualitative  Chemical  Analysis 8vo,  i  50 

Short  Course  in  Inorganic  Qualitative  Chemical  Analysis  for  Engineering 

Students i2mo,  50 

Text-book  of  Chemical  Arithmetic i2mo,  25 

Whipple's  Microscopy  of  Drinking-water 8vo,  50 

Wilson's  Chlorination  Process .  i2mo  53 

Cyanide  Processes i2mo  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo  50 


CIVIL  ENGINEERING. 

BRIDGES  AND  ROOFS.     HYDRAULICS.     MATERIALS   OF    ENGINEER- 
ING.    RAILWAY   ENGINEERING. 

Baker's  Engineers'  Surveying  Instruments 12 mo,  3  oo 

Bixby's  Graphical  Computing  Table Paper  19^X24}  inches.  25 

Breed  and  Hosmer's  Principles  and  Practice  of  Surveying .8vo,  3  oo 

*  Burr's  Ancient  and  Modern  Engineering  and  the  Isthmian  Canal 8vo,  3  50 

Comstock's  Field  Astronomy  for  Engineers 8vo,  2  50 

*  CorthelTs  Allowable  Pressures  on  Deep  Foundations I2mo,  125 

Crandall's  Text-book  on  Geodesy  and  Least  Squares .8vo,  3  oo 

Davis's  Elevation  and  Stadia  Tables 8vo,  i  oo 

Elliott's  Engineering  for  Land  Drainage i2mo,  i  50 

Practical  Farm  Drainage i2mo,  i  oo 

*Fiebeger's  Treatise  on  Civil  Engineering 8vo,  5  oo 

Flemer's  Phototopographic  Methods  and  Instruments 8vo,  5  oo 

Folwell's  Sewerage.     (Designing  and  Maintenance.) 8vo,  3  oo 

Freitag's  Architectural  Engineering 8vo,  3  50 

French  and  Ives's  Stereotomy 8vo,  2  50 

Goodhue's  Municipal  Improvements i2mo,  i  50 

Gore's  Elements  of  Geodesy 8vo,  2  50 

*  Hauch  and  Rice's  Tables  of  Quantities  for  Preliminary  Estimates, I2mo,  i  25 

Hayford's  Text-book  of  Geodetic  Astronomy 8vo,  3  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  mor.  2  50 

Howe's  Retaining  Walls  for  Earth i2mo,  i  25 


*  Ives's  Adjustments  of  the  Engineer's  Transit  and  Level  .  i i6mo,  Bds.  25 

Ives  and  Hilts's  Problems  in  Surveying i6mo,  mor.  i  50 

Johnson's  (J.  B.)  Theory  and  Practice  of  Surveying Small  8vo,  4  oo 

Johnson's  (L.  J.)  Statics  by  Algebraic  and  Graphic  Methods 8vo,  2  oo 

Kinnicutt,  Winslow  and  Pratt's  Purification  of  Sewage.     (In  Preparation). 
Laplace's    Philosophical   Essay    on    Probabilities.       (Truscott    and   Emory.) 

i2mo,  2  oo 

Mahan's  Descriptive  Geometry - 8vo,  i  50 

Treatise  on  Civil  Engineering.     (1873.)     (Wood.) 8vo,  5  oo 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy 8vo,  2  50 

Merriman  and  Brooks's  Handbook  for  Surveyors i6mo,  mor.  2  oo 

Morrison's  Elements  of  Highway  Engineering.       (In  Press.) 

Nugent's  Plane  Surveying 8vo,  3  50 

Ogden's  Sewer  Design I2mo,  2  oo 

Parsons's  Disposal  of  Municipal  Refuse 8vo,  2  oo 

Patton's  Treatise  on  Civil  Engineering 8vo,  half  leather,  7  50 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  4  oo 

Riemer's  Shaft-sinking  under  Difficult  Conditions.     (Corning  and  Peele.) .  .8vo,  3  oo 

Siebert  and  Biggin's  Modern  Stone-cutting  and  Masonry 8vo,  i  SO 

Smith's  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Soper's  Air  and  Ventilation  of  Subways.     (In  Press.) 

Tracy's  Plane  Surveying 16mo,  mor.  3  oo 

*  Trautwine's  CivM  Engineer's  Pocket-book i6mo,  mor.  5  oo 

Venable's  Garbage  Crematories  in  America 8vo,  2  oo 

Methods  and  Devices  for  Bacterial  Treatment  of  Sewage 8vo,  3  oo 

Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  oo 

Sheep,  6  50 

Law  of  Contracts 8vo,  3  oo 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  8vo,  5  oo 

Sheep,  5  5» 

Warren's  Stereotomy — Problems  in  Stone-cutting 8vo,  2  50 

*  Waterbury's  Vest-Pocket  Hand-book    of    Mathematics   for   Engineers. 

2!  X  5!  inches,  mor.  i  oo 
Webb's  Problems  in  the  Use  and  Adjustment  of  Engineering  Instruments. 

i6nio,  mor.  i  25 

Wilson's  Topographic  Surveying 8vo,  3  50 

BRIDGES  AND  ROOFS. 

Boiler's  Practical  Treatise  on  the  Construction  of  Iron  Highway  Bridges.  .8vo,  2  oo 

Burr  and  Falk's  Design  and  Construction  of  Metallic  Bridges 8vo,  5  oo 

Influence  Lines  for  Bridge  and  Roof  Computations 8vo,  3  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  II Srrall  4to,  10  oo 

Foster's  Treatise  on  Wooden  Trestle  Bridges 4to,  5  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

French  and  Ives's  Stereotomy 8vo,  2  50 

Greene's  Arches  in  Wood,  Iron,  and  Stone 8vo,  2  50 

Bridge  Trusses 8vo,  2  50 

Roof  Trusses 8vo,  i  25 

Grimm's  Secondary  Stresses  in  Bridge  Trusses 8vo,  2  50 

Heller's  Stresses  in  Structures  and  the  Accompanyin    Deformations 8vo, 

Howe's  Design  of  Simple  Roof-trusses  in  Wood  and  Steel 8vo,  2  oo 

Symmetrical  Masonry  Arches 8vo,  2  50 

Treatise  on  Arches 8vo,  4  oo 

Johnson,  Bryan,  and  Turneaure's  Theory  and  Practice  in  the  Designing  of 

Modern  Framed  Structures Small  4to,  10  oo 

7 


Merriman  and  Jacoby's  Text-book  on  Roofs  and  Bridges : 

Part  I.      Stresses  in  Simple  Trusses 8vo,  2  50 

Part  II.    Graphic  Statics 8vo,  2  50 

Part  III.  Bridge  Design 8vo,  2  50 

Part  IV.   Higher  Structures 8vo,  2  50 

Morison's  Memphis  Bridge Oblong  4to,  10  oo 

Sondericker's  Graphic  Statics,  with  Applications  to  Trusses,  Beams,  and  Arches. 

8vo,  2  oo 

Waddell's  De  Pontibus,  Pocket-book  for  Bridge  Engineers i6mo,  mor,  2  oo 

*          Specifications  for  Steel  Bridges i2mo,  50 

Waddell  and  Harrington's  Bridge  Engineering.     (In  Preparation.) 

Wright's  Designing  of  Draw-spans.     Two  parts  in  one  volume 8vo,  3  50 


HYDRAULICS. 

Barnes's  Ice  Formation 8vo,  3  oo 

Bazin's  Experiments  upon  the  Contraction  of  the  Liquid  Vein  Issuing  from 

an  Orifice.     (Trautwine.) 8vo,  2  oo 

Bovey's  Treatise  on  Hydraulics 8vo,  5  oo 

Church's  Diagrams  of  Mean  Velocity  of  Water  in  Open  Channels. 

Oblong  4to,  paper,  i  50 

Hydraulic  Motors 8vo,  2  oo 

Mechanics  of  Engineering 8vo,  6  oo 

Coffin's  Graphical  Solution  of  Hydraulic  Problems i6mo,  morocco,  2  50 

Flather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

Folwell's  Water-supply  Engineering 8vo,  4  oo 

Frizell's  Water-power 8vo,  5  oo 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Water-filtration  Works i2mo,  2  50 

Ganguillet  and  Kutter's  General  Formula  for  the  Uniform  Flow  of  Water  in 

Rivers  and  Other  Channels.     (Hering  and  Trautwine.) 8vo,  4  oo 

Hazen's  Clean  Water  and  How  to  Get  It Large  I2mo,  i  5o 

Filtration  of  Public  Water-supplies 8vo,  3  oo 

Hazlehurst's  Towers  and  Tanks  for  Water-works 8vo,  2  50 

Herschel's  115  Experiments  on  the  Carrying  Capacity  of  Large,  Riveted,  Metal 

Conduits 8vo,  2  oo 

Hoyt  and  Grover's  River  Discharge 8vo,  2  oo 

Hubbard  and  Kiersted's  Water-works  Management  and  Maintenance 8vo,  4  uo 

*  Lyndon's  Development  and  Electrical  Distribution  of  Water  Power.  .  .  .8vo,  3  oo 
Mason's  Water-supply.     (Considered  Principally  from  a  Sanitary  Standpoint.) 

.  8vo,  4  oo 

I£erriman's  Treatise  on  Hydraulics 8vo,  5  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

Molitor's  Hydraulics  of  Rivers,  Weirs  and  Sluices,     tin  Press.) 

Schuyler's   Reservoirs   for  Irrigation,   Water-power,   and   Domestic   Water- 
supply Large  8vo,  5  oo 

*  Thoma-:  and  Watt's  Improvement  of  Rivers 4to,  6  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Wegmann's  Design  and  Construction  of  Dams.     5th  Ed.,  enlarged 4to,  6  oo 

Water-supply  of  the  City  of  New  York  from  1658  to  1895 4to,  10  oo 

Whipple's  Value  of  Pure  Water Large  i2mo,  i  oo 

Williams  and  Hazen's  Hydraulic  Tables 8vo,  i  50 

Wilson's  Irrigation  Engineering Small  8vo,  4  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Turbines 8vo,  2  50 

8 


MATERIALS  OF  ENGINEERING. 

Baker's  Roads  and  Pavements 8vo,  5  oo 

Treatise  on  Masonry  Construction 8vo,  5  oo 

Birkmire's  Architectural  Iron  and  Steel 8vo,  3  50 

Compound  Riveted  Girders  as  Applied  in  Buildings 8vo,  2  oo 

Black's  United  States  Public  Works Oblong  4to,  5  oo 

Bleininger's  Manufacture  of  Hydraulic  Cement.     (In  Preparation.) 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Byrne's  Highway  Construction 8vo,  5  oo 

Inspection  of  the  Materials  and  Workmanship  Employed  in  Construction. 

i6mo,  3  oo 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Du  Bois's  Mechanics  of  Engineering. 

Vol.    I.  Kinematics,  Sratics,  Kinetics Small  4to,  7  50 

VoL  II.  The  Stresses  in  Framed  Structures,  Strength  of  Materials  and 

Theory  of  Flexures Small  4to,  10  oo 

*Eckel's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Stone  and  Clay  Products  used  in  Engineering.     (In  Preparation.) 

Fowler's  Ordinary  Foundations 8vo,  3  5° 

Graves's  Forest  Mensuration *. 8vo,  4   oo 

Green's  Principles  of  American  Forestry i2mo,  i   *o 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Holly  and  Ladd's  Analysis  of  Mixed  Paints,  Color  Pigments  and  Varnishes 

Large  i2mo,  2  50 

Johnson's  Materials  of  Construction Large  8vo,  6  oo 

Keep's  Cast  Iron 8vo,  2  50 

Kidder's  Architects  and  Builders'  Pocket-book i6mo,  5  oo 

Lanza's  Applied  Mechanics 8vo,  7  50 

Maire's  Modern  Pigments  and  their  Vehicles      i2mo,  2  oo 

Martens's  Handbook  on  Testing  Materials.     (Henning.)     2  vols 8vo,  750 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

*  Strength  of  Materials i2mo,  i  oo 

Metcalf's  Steel.     A  Manual  for  Steel-users I2mo,  2  oo 

Patton's  Practical  Treatise  on  Foundations, 8vo,  5  oo 

Rice's  Concrete  Block  Manufacture 8vo,  2  oo 

Richardson's  Modern  Asphalt  Pavements 8vo,  3  oo 

Richey's  Handbook  for  Superintendents  of  Construction i6mo,  mor.,  4  oo 

*  Ries's  Clays:  Their  Occurrence,  Properties,  and  Uses 8vo,  5  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

*Schwarz's  Longleaf  Pine  in  Virgin  Forest.. limo,  i   25 

Snow's  Principal  Species  of  Wood 8vo,  3  50 

Spalding's  Hydraulic  Cement I2mo,  2  oo 

Text-book  on  Roads  and  Pavements i2mo,  2  oo 

Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  oo 

Part  I.     Non-metallic  Materials  of  Engineering  and  Metallurgy 8vo,  2  oo 

Part  H.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Tillson's  Street  Pavements  and  Paving  Materials 8vo,  4  oo 

Turneaure  and  Maurer's  Principles  of  Reinforced  Concrete  Construction..  .8vo,  3  oo 
Wood's  (De  V.)  Treatise  on  the  Resistance  of  Materials,  and  an  Appendix  on 

the  Preservation  of  Timber 8vo,  2  oo 

Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  oo 

9 


RAILWAY  ENGIJVEERIN3. 

Andrews's  Handbook  for  Street  Railway  Engineers 3x5  inches,  mor.  i  25 

Berg's  Buildings  and  Structures  of  American  Railroads 4to,  5  oo 

Brooks's  Handbook  of  Street  Railroad  Location i6mo,  mor.  I  50 

Butt's  Civil  Engineer's  Field-book i6mo,  mor.  2  50 

CrandalTs  Railway  and  Other  Earthwork  Tables 8vo,  i  50 

Transition  Curve i6mo,  mor.  i  50 

*  Crockett's  Methods  for  Earthwork  Computations 8vo,  i  50 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book    i6mo,  mor.  5  oo 

Dredge's  History  of  the  Pennsylvania  Railroad:    (1870,) Paper,  5  oo 

Fisher's  Table  of  Cubic  Yards Cardboard,  25 

Godwin's  Railroad  Engineers'  Field-book  and  Explorers'  Guide.  .  .  i6mo,  mor.  2  50 
Hudson's  Tables  for  Calculating  the  Cubic  Contents  of  Excavations  and  Em- 
bankments  8vo,  i  oo 

Ives   and  Hilts's  Problems   in  Surveying,  Railroad   Surveying  and   Geodesy 

i6mo,  mor.  i  50 

Molitor  and  Beard's  Manual  for  Resident  Engineers i6mo,  i  oo 

Nagle's  Field  Manual  for  Railroad  Engineers i6mo,  mor.  3  oo 

Philbrick's  Field  Manual  for  Engineers i6mo,  mor.  3  oo 

Raymond's  Railroad  Engineering.     3  volumes. 

Vol.      I.  Railroad  Field  Geometry.     (In  Preparation.) 

Vol     II.  Elements  of  Railroad  Engineering 8vo,  3  50 

Vol  III.  Railroad  Engineer's  Field  Book.     (In  Preparation.) 

Searles's  Field  Engineering i6mo,  mor.  3  oo 

Railroad  Spiral i6mo,  mor.  i  50 

Taylor's  Prismoidal  Formulae  and  Earthwork 8vo,  i  50 

*Trautwine's  Field  Practice  of  Laying   Out  Circular  Curves   for  Railroads. 

i2mo.  mor,  2  50 

*  Method  of  Calculating  the  Cubic  Contents  of  Excavations  and  Embank- 

ments by  the  Aid  of  Diagrams 8vo,  2  oo 

Webb's  Economics  of  Railroad  Construction. .  . .' Large  i2mo,  2  50 

Railroad  Construction i6mo,  mor.  5  oo 

Wellington's  Economic  Theory  of  the  Location  of  Railways Small  8vo,  5  oo 

DRAWING. 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "                                                  Abridged  Ed 8vo,  i  50 

Coolidge's  Manual  of  Drawing 8vo,  paper,  i  oo 

Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  Engi- 
neers  Oblong  4to,  2  50 

Durley's  Kinematics  of  Machines 8vo,  4  oo 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications Svo,  2  50 

Hill's  Text-book  on  Shades  and  Shadows,  and  Perspective Svo,  2  oo 

Jamison's  Advanced  Mechanical  Drawing Svo,  2  oo 

Elements  of  Mechanical  Drawing Svo,  2  50 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery Svo,  i  50 

Part  II.    Form,  Strength,  and  Proportions  of  Parts Svo,  3  oo 

MacCord's  Elements  of  Descriptive  Geometry Svo,  3  oc 

Kinematics;  or,  Practical  Mechanism Svo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Velocity  Diagrams Svo,  i  50 

McLeod's  Descriptive  Geometry Large  i2mo,  i  50 

*  Mahan's  Descriptive  Geometry  and  Stone-cutting Svo,  i  50 

Industrial  Drawing.     (Thompson.) Svo,  3  50 

10 


Meyer's  Descriptive  Geometry .. 8vo,  2  oo 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (R.  S.)  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

*  Titsworth's  Elements  of  Mechanical  Drawing Oblong  8vo,  i  25 

Barren's  Drafting  Instruments  and  Operations i?mo,  i  25 

Elements  of  Descriptive  Geometry,  Shadows,  and  Perspective 8vo,  3  50 

Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Elements  of  Plane  and  Solid  Free-hand  Geometrical  Drawing.  .  .    i.2mo,  i  oo 

General  Problems  of  Shades  and  Shadows 8vo,  3  oo 

Manual  of  Elementary  Problems  in  the  Linear  Perspective  of  Form  and 

Shadow i2mo,  i  oo 

Manual  of  Elementary  Projection  Drawing i2mo,  i  50 

Plane  Problems  in  Elementary  Geometry i2mo,  i  25 

Problems,  Theorems,  and  Examples  in  Descriptive  Geometry 8vo,  2  50 

Weisbach's    Kinematics    and    Power    of    Transmission.        (Hermann    and 

Klein.) 8vo,  5  oo 

Wilson's  (H.  M.)  Topographic  Surveying 8vo,  3  50 

Wilson's  (V.  T.)  Free-hand  Lettering 8vo,  i  oo 

Free-hand  Perspective 8vo,  2  50 

Woolf's  Elementary  Course  in  Descriptive  Geometry Large  8vo,  3  oo 

ELECTRICITY  AND  PHYSICS. 

*  Abegg's  Theory  of  Electrolytic  Dissociation,     (von  Ende.) i2mo,  i   25 

Andrews's  Hand-Book  for  Street  Railway  Engineering  ...  .3X5  inches,  mor.,  i  25 

Anthony  and  Brackett's  Text-book  of  Physics.     (Magie.) Large  I2mo,  3  oo 

Anthony's  Lecture-notes  on  the  Theory  of  Electrical  Measurements.  .  .  .i2mo,  i  oo 

Benjamin's  History  of  Electricity 8vo,  3  oo 

Voltaic  CelL 8vo,  3  oo 

Betts's  Lead  Refining  and  Electrolysis 8vo,  4  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.     (Boltwood.).8vo,  3  oo 

*  Collins's  Manual  of  Wireless  Telegraphy i2mo,  i  50 

Mor.  2  oo 

Crehore  and  Squier's  Polarizing  Photo-chronograph 8vo,  3  oo 

*  Danneel's  Electrochemistry.     (Merriam.) i2mo,  i  25 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book i6mo,  mor  5  oo 

Dolezalek's  Theory  of  the  Lead  Accumulator  (Storage  Battery),    (von  Ende.) 

i2mo,  2  50 

Duhem's  Thermodynamics  and  Chemistry.     (Burgess.) 8vo,  4  oo 

Flather's  Dynamometers,  and  the  Measurement  of  Power 12 mo,  3  oo 

Gilbert's  De  Magnete.     (Mottelay.) 8vo,  2  50 

*  Hanchett's  Alternating  Currents I2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  mor.  2  50 

Hobart  and  Ellis's  High-speed  Dynamo  Electric  Machinery.     (In  Press.) 

Holman's  Precision  of  Measurements 8vo,  2  oo 

Telescopic   Mirror-scale  Method,  Adjustments,  and  Tests. ..  .Large  8vo,  75 

*  Karapetoff's  Experimental  Electrical  Engineering 8vo,  6  oo 

Kinzbrunner's  Testing  of  Continuous-current  Machines 8vo,  2  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess.)  i2mo,  3  oo 

Lob's  Electrochemistry  of  Organic  Compounds.     (Lorenz.) ;  .8vo,  3  oo 

*  London's  Development  and  Electrical  Distribntion  of  Water  Power  .  . .  .8vo,  3  oo 

*  Lyons'?  Treatise  on  Electromagnetic  Phenomena.   Vols.  I.  and  II.  8vo,  each,  6  oo 

*  Michie's  Elements  of  Wave  Motion  Relating  to  Sound  and  Light 8vo,  4  co- 

ll 


Morgan's  Outline  of  the  Theory  of  Solution  and  its  Results i2mo,  i  oo 

*  Physical  Chemistry  for  Electrical  Engineers i2mo,  i  50 

Niaudet's  Elementary  Treatise  on  Electric  Batteries.     (Fishback).  .  .  .  izmo.  2  50 

*  Norris's  Introduction  to  the  Study   of  Electrical  Engineering Svo,  2  50 

*  Parshall  and  Hobart's  Electric  Machine  Design 4to,  half  morocco,  12  50 

Reagan's  Locomotives:    Simple,  Compound,  and  Electric.      New  Edition. 

Large  12010,  3  50 

*  Rosenberg's  Electrical  Engineering.     (Haldane  Gee — Kinzbrunner.).  .  .8vo,  2  oo 

Ryan,  Norris,  and  Hoxie's  Electrical  Machinery.     Vol.  1 8vo,  2  50 

Sjhapper's  Laboratory  Guide  for  Students  in  Physical  Chemistry i2mo,  i  oo 

Thurston's  Stationary  Steam-engines 8vo,  2  50 

*  Tillman's  Elementary  Lessons  in  Heat 8vo,  i  50 

Tory  and  Pitcher's  Manual  of  Laboratory  Physics Large  i2mo,  2  oo 

Ulke's  Modern  Electrolytic  Copper  Refining Svo,  3  oo 

LAW. 

*  Davis's  Elements  of  Law Svo,    2  50 

*  Treatise  on  the  Military  Law  of  United  States Svo,    7  oo 

*  Sheep,     7  50 

*  Dudley's  Military  Law  and  the  Procedure  of  Courts-martial  .  . .  .Large  i2mo,     2  50 

Manual  for  Courts-martial i6mo,  mor.     i  50 

Wait's  Engineering  and  Architectural  Jurisprudence < Svo,    6  oo 

Sheep,     6  50 

Law  of  Contracts Svo,    3  oo 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  Svo      5  oo 

Sheep,    5  50 
MATHEMATICS. 

Baker's  Elliptic  Functions Svo, 

Briggs's  Elements  of  Plane  Analytic  Geometry.    (Bocher) i2mo, 

*  Buchanan's  Plane  and  Spherical  Trigonometry Svo, 

Byerley's  Harmonic  Functions Svo, 

Chandler's  Elements  of  the  Infinitesimal  Calculus 12 mo, 

Compton's  Manual  of  Logarithmic  Computations i2mo, 

Davis's  Introduction  to  the  Logic  of  Algebra Svo, 

*  Dickson's  College  Algebra Large  i2mo, 

*  Introduction  to  the  Theory  of  Algebraic  Equations Large  i2mo, 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications Svo, 

Fiske's  Functions  of  a  Complex  Variable Svo, 

Halsted's  Elementary  Synthetic  Geometry Svo, 

Elements  of  Geometry Svo, 

*  Rational  Geometry i2mo, 

Hyde's  Grassmann's  Space  Analysis Svo,        oo 

*  Jonnson's  (J   B.)  Three-place  Logarithmic  Tables:  Vest-pocket  size,  paper,         15 

100  copies,     5  oo 

*  Mounted  on  heavy  cardboard,  8  X 10  inches,         25 

10  copies,  2  oo 
Johnson's  (W.  W.)  Abridged  Editions  of  Differential  and  Integral  Calculus 

Large  i2mo,  i  vol.  2  50 

Curve  Tracing  in  Cartesian  Co-ordinates i2mo,  i  oo 

Differential  Equations Svo,  i  oo 

Elementary  Treatise  on  Differential  Calculus.     (In  Press.) 

Itlcc  icntary  Treatise  on  the  Integral  Calculus Large  i2mo^  i  50 

*  Theoretical  Mechanics i2mo,  3  oo 

Theory  of  Errors  and  the  Method  of  Least  Squares i2mo,  i  50 

Treatise  on  Differential  Calculus Large  i2mo,  3  oo 

Treatise  on  the  Integral  Calculus Large  i2mo,  3  oo 

Treatise  on  Ordinary  and  Partial  Differential  Equations. .  Large  12010,  3  50 

12 


taplace's  Philosophical  Essay  on  Probabilities.     (Truscott  and  Emory.)-i2mo,     2  oo 

*  Ludlow  and  Bass's  Elements  of  Trigonometry  and  Logarithmic  and  Other 

Tables 8vo,     3  oo 

Trigonometry  and  Tables  published  separately Each,     2  oo 

*  Ludlow's  Logarithmic  and  Trigonometric  Tables 8vo,     i  oo 

Macfarlane's  Vector  Analysis  and  Quaternions 8vo,    i  oo 

McMahon's  Hyperbolic  Functions 8vo,     i  oo 

Manning's  IrrationalNumbers  and  their  Representation  bySequences  and  Series 

i2mo,     i   25 
Mathematical  Monographs.     Edited  by  Mansfield  Merriman  and  Robert 

S.  Woodward '. Octavo,  each     i  oo 

No.  i.  History  of  Modern  Mathematics,  by  David  Eugene  Smith. 
No.  2.  Synthetic  Projective  Geometry,  by  George  Bruce  Halsted. 
No.  3.  Determinants,  by  Laenas  Gifford  Weld.  No.  4.  Hyper- 
bolic Functions,  by  James  McMahon.  Ko.  5.  Harmonic  Func- 
tions, by  William  E.  Byerly.  No.  6.  Grassmann's  Space  Analysis, 
by  Edward  W.  Hyde.  No.  7.  Probability  and  Theory  of  Errors, 
by  Robert  S.  Woodward.  No.  8.  Vector  Analysis  and  Quaternions, 
by  Alexander  Macfarlane.  No.  9.  Differential  Equations,  by 
William  Woolsey  Johnson.  No.  10.  The  Solution  of  Equations, 
by  Mansfield  Merriman.  No.  n.  Functions  of  a  Complex  Variable, 
by  Thomas  S.  Fiske. 

Maurer's  Technical  Mechanics 8vo,    4  oo 

Menlman's  Method  of  Least  Squares 8vo,    2  oo 

Solution  of  Equations 8vo,     I  oo 

Rice  and  Johnson's  Differential  and  Integral  Calculus.     2  vols.  in  one. 

Large  12 mo,     i  50 

Elementary  Treatise  on  the  Differential  Calculus Large  12010,     3  oo 

Smith's  History  of  Modern  Mathematics 8vo,     i  oo 

*  Veblen  and  Lennes's  Introduct-on  to  the  Real  Infinitesimal  Analysis  of  One 

Variable 8vo,    2  oo 

*  Waterbury's  Vest  Pocket  Hand-Book  of  Mathematics  for  Engineers. 

24X5!  inches,  mor.,    i  oo 

Weld's  Determinations 8vo,     i  oo 

Wood's  Elements  of  Co-ordinate  Geometry 8vo,    2  oo 

Woodward's  Probability  and  Theory  of  Errors 8vo,    i  oo 

MECHANICAL  ENGINEERING. 

MATERIALS   OF   ENGINEERING,  STEAM-ENGINES  AND  BOILERS. 

Bacon's  Forge  Practice i2mo,  i  50 

Baldwin's  Steam  Heating  for  Buildings i2mo,  2  50 

Bair's  Kinematics  of  Machinery 8vo,  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "  "  "        Abridged  Ed 8vo,    150 

Benjamin's  Wrinkles  and  Recipes i2mo,    2  oo 

*  Burr's  Ancient  and  Modern  Engineering  and  the  Isthmian  Canal 8vo,    3  50 

Carpenter's  Experimental  Engineering 8vo,    6  oo 

Heating  and  Ventilating  Buildings 8vo,  4  oo 

Clerk's  Gas  and  Oil  Engine Large  i2mo,  4  oo 

Compton's  First  Lessons  in  Metal  Working I2mo,  i  50 

Compton  and  De  Groodt's  Speed  Lathe 12mo,  i  50 

Coolidge's  Manual  of  Drawing 8vo,  paper,  i  oo 

Ccolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  En- 
gineers   Oblong  4to,  2  50 

Cromwell's  Treatise  on  Belts  and  Pulleys 1 2mo,  i  50 

Treatise  on  Toothed  Gearing I2mo,  i  50 

Durley*s  Kinematics  of  Machines 8vo,  4  oo 

13 


Flather's  Dynamometers  and  the  Measurement  of  Power, 12010,  3  oo 

Rope  Driving i2mo,  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers 12010,  i  25 

Goss'r;  Locomotive  Sparks 8vo,  2  oo 

Hall's  Car  Lubrication i2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  mor.,  2  50 

Hobart  and  Elds's  High  Speed  Dynamo  Electric  Machinery.      (In  Press.) 

Button's  Gas  Engine 8vo,  5  oo 

Jamison's  Advanced  Mechanical  Drawing 8vo,  2  oo 

Elements  of  Mechanical  Drawing 8vo,  2  50 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

Kent's  Mechanical  Engineers'  Pocket-book i6mo,  mor  ,  5  oo 

Kerr's  Power  and  Power  Transmission 8vo,  2  oo 

Leonard's  Machine  Shop  Tools  and  Methods   8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.    (Pope,  Haven,  and  Dean.)  .  .8vo,  4  oo 
MacCord's  Kinematics;   or,  Practical  Mechanism 8vo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Velocity  Diagrams 8vo,  i  30 

MacFarland's  Standard  Reduction  Factors  for  Gases 8vo,  i  50 

Mahan's  Industrial  Drawing.     (Thompson.) 8vo,  3  50 

*  Parshall  and  Hobart's  Electric  Machine  Design Small  4to,  half  leather,   12  50 

Peele's  Compressed  Air  Plant  for  Mines.     (In  Press.) 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oo 

*  Porter's  Engineering  Reminiscences,  1855  to  1882 8vo,  3  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Richard's  Compressed  Air i2mo,  i  50 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (O.)  Press- working  of  Metals 8vo,  3  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design " 8vo,  3  oo 

Sorel '  s  Carbureting  and  Combustion  in  Alcohol  Engines .    (Woodward  and  Preston) . 

Large  12 mo,  3  oo 
Thurston's  Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics. 

i2mo,  i  oo 

Treatise  on  Friction  and  Lost  Work  in  Machinery  and  Mill  Work...  8vo,  3  oo 

Tillson's  Complete  Automobile  Instructor i6mo,  i   50 

mor.,  2  oo 

*  Titsworth's  Elements  of  Mechanical  Drawing Oblong  8vo,  i    25 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

*  Waterbury's  Vest  Pocket  Hand  Book  of  Mathematics  for  Engineers. 

2tX  5s  inches,  mor.,  i   oo 
Weisbach's    Kinematics    and    the    Power    of    Transmission.     (Herrmann — 

Klein.) 8vo,  5  oo 

Machinery  of  Transmission  and  Governors.     (Herrmann — Klein.).  .8vo,  5  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 

MATERIALS   OF   ENGINEERING. 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Church's  Mechanics  of  Engineering.' 8vo,  6  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Holley  and  Ladd's  Analysis  of  Mixed  Paints,  Color  Pigments,  and  Varnishes. 

Large  i2mo,  2  50 

Johnson's  Materials  of  Construction 8vo,  6  oo 

Keep's  Cast  Iron 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

14 


Maire's  Modern  Pigments  and  their  Vehicles i2mo,  2  oo 

Martens 's  Handbook  on  Testing  Materials.     (Henning.) 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

*         Strength  of  Materials •. I2mo,  i  oo 

Metcalf 's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish. 8vo,  3  oo 

Smith's  Materials  of  Machines I2mo,  i  oo 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  oo 

Part  I.     Noa-metallic  Materials  of  Engineering,  see  Civil  Engineering, 
page  9. 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents Svo,  2  50 

Wood's  (De  V.)  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Treatise  on    the    Resistance    of    Materi-ls  and   an  Appendix  on  the 

Preservation  of  Timber 8vo,  a  oo 

Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  oo 

STEAM-ENGINES  AND  BOILERS. 

Berry's  Temperature-entropy  Diagram I2mo,  i  25 

Carnot's  Reflections  on  the  Motive  Power  of  Heat.     (Thurston.) i2mo,  i  50 

Chase's  Art  of  Pattern  Making i2mo,  2  50 

Creighton's  Steam-engine  and  other  Heat-motors         8vo,  500 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book.  . .  .i6mo,  mor.,  5  oo 

Ford's  Boiler  Making  for  Boiler  Makers i8mo,  i  oo 

Goss's  Locomotive  Performance 8vo,  5  oo 

Hemenway's  Indicator  Practice  and  Steam-engine  Economy. i2mo,  2  oo 

Button's  Heat  and  Heat-engines 8vo,  5  oo 

Mechanical  Engineering  of  Power  Plants 8vo,  5  oo 

Kent's  Steam  boiler  Economy 8vo,  4  oo 

Kneass's  Practice  and  Theory  of  the  Injector Svo,  i  50 

MacCord's  Slide-valves Svo,  2  co 

Meyer's  Modern  Locomotive  Construction 4to,  10  oo 

Meyer's  Steam  Turbines.     (Tn  Press.) 

Peabody's  Manual  of  the  Steam-engine  Indicator I2mo.  i  50 

Tables  of  the  Properties  of  Saturated  Steam  and  Other  Vapors   Svo,  i  oo 

Thermodynamics  of  the  Steam-engine  and  Other  Heat-engines Svo,  5  oo 

Valve-gears  for  Steam-engines Svo,  2  50 

Peabody  and  Miller's  Steam-boilers Svo,  4  oo 

Pray's  Twenty  Years  with  the  Indicator Large  Svo,  2  50 

Pupin's  Thermodynamics  of  Reversible  Cycles  in  Gases  and  Saturated  Vapors. 

(Osterberg.) i2mo,  i  25 

Reagan's  Locomotives:    Simple,  Compound,  and  Electric.     New  Edition. 

Large  12 mo,  3  50 

Sinclair's  Locomotive  Engine  Running  and  Management I2mo,  2  oo 

Smart's  Handbook  of  Engineering  Laboratory  Practice I2mo,  2  50 

Snow's  Steam-boiler  Practice Svo,  3  oo 

Spangler's  Notes  on  Thermodynamics I2mo,  i  oo 

Valve-gears Svo,  2  50 

Spaagler,  Greene,  and  Marshall's  Elements  of  Steam-engineering Svo,  3  oo 

Thomas's  Steam-turbines Svo,  4  oo 

Thurston's  Handbook  of  Engine  and  Eoilcr  Trials,  and  the  Use  of  the  Indi- 
cator and  the  Prony  Brake 8vo,  5  oo 

Handy  Tables Svo,  i  50 

Manual  of  Steam-boilers,  their  Designs,  Construction,  and  Operation.. Svo,  5  oo 

15 


Thurston's  Manual  of  the  Steam-engine 2  vols.,  8vo,  10  oo 

Part  I.     History,  Structure,  and  Theory 8vo,  6  oo 

Part  II.     Design,  Construction,  and  Operation 8vo,  6  oo 

Stationary  Steam-engines 8vo,  2  50 

Steam-boiler  Explosions  in  Theory  and  in  Practice 12mo,  i  50 

Wehrenfenning's  Analysis  and  Softening  of  Boiler  Feed-water  (Patterson)   8vo,  4  oo 

Weisbach's  Heat,  Steam,  and  Steam-engines.     (Du  Bois.) 8vo,  5  oo 

Whitham's  Steam-engine  Design 8vo,  5  oo 

Wood's  Thermodynamics,  Heat  Motors,  and  Refrigerating  Machines.  ..8vo,  4  oo 

MECHANICS  PURE  AND  APPLIED. 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Notes  and  Examples  in  Mechanics 8vo,  2  oo 

Dana's  Text-boofc  of  Elementary  Mechanics  for  Colleges  and  Schools.  .i2mo,  i  50 
Du  Bois's  Elementary  Principles  of  Mechanics : 

Vol.      I.     Kinematics 8vo,  3  50 

Vol.    II.     Statics 8vo,  4  oo 

Mechanics  of  Engineering.     Vol.    I Small  4to,  7  50 

Vol.  II Small  4to,  10  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

James's  Kinematics  of  a  Point  and  the  Rational  Mechanics  of  a  Particle. 

Large  12mo,  2  oo 

*  Johnson's  (W.  W.)  Theoretical  Mechanics 12mo,  3  oo 

Lanza's  Applied  Mechanics 8vo,  7  50 

*  Martin's  Text  Book  on  Mechanics,  Vol.  I,  Statics 12mo,  i   25 

*  Vol.  2,  Kinematics  and  Kinetics  .  .I2mo,     l  50 
Maurer's  Technical  Mechanics 8vo,    4  oo 

*  Merriman's  Elements  of  Mechanics 12mo,     i  oo 

Mechanics  of  Materials 8vo,  5  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Sanborn's  Mechanics  Problems Large  12mo,  i  50 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Wood's  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Principles  of  Elementary  Mechanics 12mo,     i  25 

MEDICAL. 

Abderhalden's  Physiological  Chemistry  in  Thirty  Lectures.     (Hall  and  Defren). 

(In  Press). 
von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) i2mo,     i  oo 

*  Bolduan's  Immune  Sera i2mo,     i  50 

Davenport's  Statistical  Methods  with  Special  Reference  to  Biological  Varia- 
tions   1 6mo ,  mor. ,     i   50 

Ehrlich's  Collected  Studies  on  Immunity.     (Bolduan.) 8vo,  6  oo 

*  Fischer's  Physiology  of  Alimentation Large  i2mo,  cloth,  2  oo 

de  Fursac's  Manual  of  Psychiatry.     (Rosanoff  and  Collins.) Large  i2mo,  2  50 

Hammarsten's  Text-book  on  Physiological  Chemistry.     (Mandel.) 8vo,  4  oo 

Jackson's  Directions  for  Laboratory  Work  in  Physiological  Chemistry.  ..8vo,  i  25 

Lassar-Cohn's  Practical  Urinary  Analysis.     (Lorenz.) i2mo,  i  oo 

Mandel's  Hand  Book  for  the  Bio-Chemical  Laboratory i2mo,  i  50 

*  Pauli's  Physical  Chemistry  in  the  Service  of  Medicine.     (Fischer.) .  .  .  .  i2mo,  i  25 

*  Pozzi-Escot's  Toxins  and  Venoms  and  their  Antibodies.     (Cohn.) i2mo,  i  oo 

Rostoski's  Serum  Diagnosis.     (Bolduan.) i2mo,  I  oo 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  oo 

Whys  in  Pharmacy I2mo,  i  oo 

Salkowski's  Physiological  and  Pathological  Chemistry.     (Orndorff.) 8vo,  2  50 

*  Satterlee's  Outlines  of  Human  Embryology i2mo,  i  25 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students 8vo,  2  50 

16 


Steel's  Treatise  on  the  Diseases  of  the  Dog 8vo,  3  50 

*  Whipple's  Typhoid  Fever '. Large  12 mo,  3  oo 

Woodhull's  Notes  on  Military  Hygiene i6mo,  i  50 

*  Personal  Hygiene i2mo,  i  oo 

Worcester  and  Atkinson's  Small  Hospitals  Establishment  and  Maintenance, 

and  Sjggestions  for  Hospital  Architecture,  with  Plans  for  a  Small 

Hospital i2mo ,  i  25 

METALLURGY. 

Betts's  Lead  Refining  by  Electrolysis 8vo.  4  oo 

Holland's  Encyclopedia  of  Founding  and  Dictionary  of  Foundry  Terms    Used 

in  the  Practice  of  Moulding 12mo,  3  oo 

Iron  Founder 12mo.  2  50 

"         "       Supplement 12mo,  2  50 

Douglas's  Untechnical  Addresses  on  Technical  Subjects I2mo,  i  oo 

Goesel's  Minerals  and  Metals:     A  Reference  Book i6mo,  mor.  3  oo 

*  Iles's  Lead-smelting 12mo,  2  50 

Keep's  Cast  Iron 8vo,  2  50 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess.)  12 mo,  3  oo 

Metcalf's  SteeL     A  Manual  for  Steel-users 12mo,  2  oo 

Miller's  Cyanide  Process 12mo  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.)..    .  12mo,  2  50 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Ruer's  Elements  of  Metallography.     (Mathewson).     (In  Press.) 

Smith's  Materials  of  Machines 12mo,  i  oo 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  oo 

part  I.     Non-metallic  Materials  of  Engineering,  see  Civil  Engineering, 
page  9. 

Part    II.     Iron  and  SteeL 8vo,  3  50 

Part  HL     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  tneir 

Constituents 8vo,  2  50 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 

West's  American  Foundry  Practice I2mo,  2  50 

Moulders  Text  Book 12mo,  2  50 

Wilson's  Chlorination  Process 12mo,  i  50 

Cyanide  Processes 12mo,  i  50 

MINERALOGY. 

Barringer's  Description  of  Minerals  of  Commercial  Value.    Oblong,  morocco,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vo  3  oo 

Boyd's  Map  of  Southwest  Virginia Pocket-book  form.  2  oo 

*  Browning's  Introduction  to  the  Rarer  Elements 8vo,  i  50 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.) 8vo,  4  oo 

Butler's  Pocket  Hand-Book  of  Minerals 16mo,  mor.  3  oo 

Chester's  Catalogue  of  Minerals 8vo,  paper,  i  oo 

Cloth,  i  25 

Crane '  s  Gold  and  Silv  er .     ( I  n  Press . ) 

Dana's  First  Appendix  to  Dana's  New  "  System  of  Mineralogy,  .f.  .Large  8vo,  i  oo 

Manual  of  Mineralogy  and  Petrography I2mo  2  ">o 

Minerals  and  How  to  Study  Them I2mo,  i  50 

System  of  Mineralogy Large  8vo,  half  leather,  12  50 

Text-book  of  Mineralogy 8vo,  4  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects I2mo,  i  oo 

Eakle's  Mineral  Tables 8vo,  i  25 

Stone  and  Clay  Products  Used  in  Engineering.     (In  Preparation). 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Goesel's  Minerals  and  Metals :     A  Reference  Book 1 6mo ,  mor.  3  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) 12010,  i  25 

17 


*  Iddings's  Rock  Minerals 8vo,  5  oo 

Johannsen's  Determination  of  Rock-forming  Minerals  in  Thin  Sections 8vo,  4  oo 

*  Martin's  Laboratory  Guide  to  Qualitative  Analysis  with  the  Blowpipe,  lamo,  60 
Merrill's  Non-metallic  Minerals:  Their  Occurrence  and  Uses  ... 8vo,  4  oo 

Stones  for  Building  and  Decoration 8vo,  500 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

8vo,  paper,  50 
Tables    of    Minerals,    Including   the  Use  of  Minerals  and  Statistics  of 

Domestic  Production 8vo,  i  oo 

Pirsson's  Rocks  and  Rock  Minerals.     (In  Press.) 

*  Richards's  Synopsis  of  Mineral  Characters i2mo,  mor.  i  25 

*  Ries's  Clays:  Their  Occurrence,  Properties,  and  Uses 8vo,  5  oo 

*  Tillman's  Text-book  of  Important  Minerals  and  Rocks. 8vo,  2  oo 

MINING. 

*  Beard's  Mine  Gases  and  Explosions Large  i2mo,  3  oo 

Boyd's  Map  of  Southwest  Virginia Pocket-book  torm,  2  oo 

Resources  of  Southwest  Virginia 8vo,  3  oo 

Crane's  Gold  and  Silver.     (In  Press.) 

Douglas's  Untechnical  Addresses  on  Technical  Subjects I2mo,  I  OO 

Eissler's  Modern  High  Explosives 8vo  4  oo 

Goesel's  Minerals  and  Metals :     A  Reference  Book i6mo,  mor.  3  oo 

Ihlseng's  Manual  of  Mining 8vo,  5  OO 

*  Iles's  Lead-smelting I2mo,  2  50 

Miller's  Cyanide  Process i2mo,  i  oo 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Peele's  Compressed  Air  Plant  for  Mines.     (In  Press.) 

Riemer's  Shaft  Sinking  Under  Difficult  Conditions.     (Corning  and  Peele) . .  .8vo,  3  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

*  Weaver's  Military  Explosives 8vo,  3  oo 

Wilson's  Chlorination  Process i^rno,  i  50 

Cyanide  Processes i2mo,  i  50 

Hydraulic  and  Placer  Mining.     2d  edition,  rewritten i2mo,  2  50 

Treatise  on  Practical  and  Theoretical  Mine  Ventilation i2mo,  i  23 

SANITARY  SCIENCE. 

Association  of  State  and  National  Food  and  Dairy  Departments,  Hartford  Meeting, 

1906 8vo,  3  oo 

Jamestown  Meeting,  1907 8vo,  3  oo 

*  Bashore's  Outlines  of  Practical  Sanitation 12mo,  i  25 

Sanitation  of  a  Country  House 12mo,  i  oo 

Sanitation  of  Recreation  Camps  and  Parks 12mo,  i  oo 

Folwell's  Sewerage.  (Designing,  Construction,  and  Maintenance.;.  ...  .8vo,  3  oo 

Water-supply  Engineering 8vo,  4  oo 

Fowler's  Sewage  Works  Analyses 12mo,  2  oo 

Fuertes's  Water-filtration  Works 12mo,  2  50 

Water  and  Public  Health 12mo,  i  50 

Gerhard's  Guide  to  Sanitary  House-inspection 16mo,  i  oo 

*  Modern  Baths  and  Bath  Houses   8vo,  3  oo 

Sanitation  of  Public  Buildings ...  I2mo,  i  50 

Hazen's  Clean  Water  and  How  to  Get  It L^rge  I2mo,  i  50 

Filtration  of  Public  Water-supplies 8vo,  3  oo 

Kinnicut,  Winslow  and  Pratt's  Purification  of  Sewage.     (In  Press. ) 

Leach's   Inspection   and   Analysis  of  Food  with  Special  Reference   to  State 

Control 8vo,  7  oo 

Mason's  Examination  of  Water.     (Chemical  a -d  Bacteriological) 12mo,  i  25 

Water-supply.  (Considered  principally  from  a  Sanitary  Standpoint).  .8vo,  4.  oo 

18 


*  Merriman's  Elements  of  Sanitary  Engineering . . . . , 8vo,    a  oo 

Ogden's  Sewer  Design I2mo,    2  oo 

Parsor\s's  Disposal  of  Municipal  Refuse 8vo,     2  oo 

Prescott  and  Winslow's  Elements  of  V/ater  Bacterielogy,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis 12mo, 

*  Price's  Handbook  on  Sanitation 12mo, 

Richards's  Cost  of  Food.     A  Study  in  Dietaries 12mo, 


Cost  of  Living  as  Modi^ed  by  Sanitary  Science 12mo, 


So 
50 
oo 
oo 

Cost  of  Shelter 12mo,  oo 

*  Richards  and  Williams's  Dietary  Computer 8vo,  50 

Richards  and   Woodman's  Air,  Water,  and  Food  from  a  Sanitary  Stand- 
point  8vo,  2  oo 

Rideal's  Disinfection  and  the  Preservation  of  Food 8vo,  4  oo 

Sewage  and  Bacterial  Purification  of  Sewage 8vo,  4  oo 

Soper's  Air  and  Ventilation  of  Subways.     (In  Press.) 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Venable's  Garbage  Crematories  in  America 8vo,  2  oo 

Method  and  Devices  for  Bacterial  Treatment  of  Sewage 8vo,  3  oo 

Ward  and  Whipple '  s  Freshwater  Biology .     (In  Press . ) 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

*  Typhod  Fever Large  I2mo,  3  oo 

Value  of  Pure  Water Large  I2mo,  i  oo 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  So 

MISCELLANEOUS. 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Excursion  of  the 

International  Congress  of  Geologists Large  8vo,  i  50 

Fen-el's  Popular  Treatise  on  the  Winds 8vo,  4  oo 

Fitzgerald's  Boston  Machinist i8mo,  i  OD 

Gannett's  Statistical  Abstract  of  the  World 24mo,  75 

Haines's  American  Railway  Management 12mo,  2  50 

*  Hanusek's  The  Microscopy  of  Technical  Products.     (Winton 8vo,  5  oo 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute   1824-1894. 

Large  12 mo,  3  oo 

Rotherham's  Emphasized  New  Testament , Large  8vo,  2  oo 

Standage's  Decoration  of  Wood,  Glass,  Metal,  etc 12mo,  2  oo 

Thome's  Structural  and  Physiological  Botany.    (Bennett) 16mo,  2  25 

Westermaier's  Compendium  of  General  Botany.     (Schneider) 8vo,  2  oo 

Winslow's  Elements  of  Applied  Microscopy 12mo,  i  50 


HEBREW  AND  CHALDEE  TEXT-BOOKS. 

Green's  Elementary  Hebrew  Grammar 12 mo,     i  25 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament  Scriptures. 

(Tregelles.) Small  4to,  half  morocco,    5  oo 

19 


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